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Name
Caesar himself does not give a name for this battle. However his continuator, the anonymous author of the Alexandrian War (probably Aulus Hirtius), is a contemporary source for the name "Battle of Pharsalus" (42, "ex fuga Pharsalici proeli"). But other ancient writers place the battle at  Palaepharsalos, "Old Pharsalus", or refer to "Pharsalia", meaning the district of Pharsalus rather than the city itself.

Combatants
Caesarian Roman (C. Iulius Caesar) vs Pompeian, "Republican", or "Optimate" Roman (Cn. Pompeius Magnus)

Background
The climactic battle of the great Roman Civil War. Caesar had won control of Italy and pursued Pompey to Greece. After indecisive fighting around Dyrrachium on the Adriatic, both armies marched inland in search of supplies and met near Pharsalus in Thessaly.

Numbers reported
Caesar: 22,000 legionaries (plus camp-guard), 1,000 German and Gallic cavalry with supporting infantry, a few thousand (?) light infantry.
Pompey: 47,000 legionaries (45,000 plus 2,000 evocati veterans; plus camp-guard), 7,000 Roman and allied cavalry, numerous light infantry.

Sources
As befits such an important encounter there are several ancient accounts. The most detailed and important is the victorious commander Julius Caesar's Civil War, Book III. Other accounts include Appian's Civil Wars, Plutarch's Lives of both Caesar and Pompey (and a brief reference in the Life of Antony), Dio Cassius, and Lucan's epic poem Pharsalia. There are shorter accounts or anecdotes, some of them apparently taken from the main sources, in Fronto, Orosius, Frontinus, Polyaenus, and probably other writers.

Source account
Caesar, Civil War, III.84-99 (from the Loeb translation of 1914):

84: When he had arranged for his corn supply and had encouraged his soldiers and had allowed a sufficient time to elapse after the battles of Dyrrachium to admit of his feeling assured of the temper of his troops, Caesar thought it right to find out what purpose or what disposition for fighting Pompeius had. And so he led his army out of the camp and drew up his lines, first of all in a position favourable to himself and some little distance from the camp of Pompeius, but on subsequent days advancing away from his own camp and pushing his line up to the foot of the hills held by the Pompeians. This action made his army day by day more confident. But in the case of his cavalry he retained his previous custom which we have explained above: since they were many times inferior in number, he gave orders that lightly equipped youths from among the first-rank men (adulescentes atque expeditos ex antesignanis), with arms selected with a view to fleetness (electis ad pernicitatem armis), should go into battle among the cavalry, so that by daily practice they might win experience in this kind of fighting also. The result of these measures was that one thousand horsemen, even in the more open ground, ventured, with the experience they had gained, to sustain the attack of seven thousand Pompeian horse, and were not greatly terrified by their multitude. For even on those days he fought a successful cavalry skirmish and killed among some others one of the two Allobrogians who, as we explained above, had deserted to Pompeius.

85: Pompeius, who had his camp on the hill, kept drawing up his line on the lowest spurs of the mountain, apparently always waiting to see whether Caesar would approach close up to the unfavourable ground. Caesar, thinking that Pompeius could by no means be enticed out to a battle, judged that his most convenient plan of campaign was to move his camp from that place, and to be always on the march, with the view of getting his supplies more conveniently by moving camp and visiting various places and at the same time of meeting with some opportunity of fighting on the route, and of wearing out the army of Pompeius, which was unaccustomed to hard work, by daily marches. After making these arrangements, when the signal for starting had now been given and the tents had been unstretched, it was noticed that a little while before, contrary to its daily custom, Pompeius' line had advanced somewhat further from the rampart, so that it seemed possible for a battle to be fought in no disadvantageous position. Then Caesar, addressing his men, when his force was just at the gates, said: "We must put off our march for the present and think of giving battle, as we have always demanded. Let us be prepared in heart for a conflict; we shall not easily hereafter find an opportunity." At once he leads out his troops in light order (expeditas).

86: Pompeius, too, as was found out afterwards, had determined, with the general encouragement of his men, to fight a pitched battle. For he had gone so far as to assert in the council of war on previous days that Caesar's army would be repulsed before the lines met. When several had expressed their surprise at this: "I know," said he, "that I am promising a thing almost incredible, but listen to the nature of my plan that you may go forth to battle with a stouter heart. I have induced my cavalry — and they have assured me that they will do it — as soon as the two armies have drawn nearer, to attack Caesar's right wing on his open flank, and by surrounding his column from the rear to drive his army in confused rout before a weapon is cast at the foe by us. So we shall finish the war without imperilling the legions and almost without a wound. And this is not difficult, considering that we are so strong in cavalry." At the same time he urged upon them that they should be strong in spirit for the coming day, and since they had now the opportunity for fighting which they had often demanded, they should not disappoint either his expectation or that of the rest.

87: Labienus followed him. [speech omitted]

88: Caesar, having approached the camp of Pompeius, observed that his [Pompey's] line was drawn up as follows: On the left wing were the two legions which had been handed over by Caesar at the beginning of the civil strife by decree of the senate, one of which was called the First, the other the Third. At that place was Pompeius himself. Scipio occupied the middle of the line with the Syrian legions. The Cilician legion, united with the Spanish cohorts, which, as we explained, had been brought over by Afranius, was stationed on the right wing. These legions Pompeius regarded as the strongest under his command. The rest he had interposed between the centre and the wings and had made up the number of one hundred and ten cohorts. These forces amounted to forty-five thousand men, and about two thousand "evocati" who had come to him from the "beneficiarii" of his former armies; and these he had distributed throughout the whole force. Seven remaining cohorts he had placed on garrison duty in the camp and the neighbouring forts. A stream with difficult banks protected his right wing; for which reason he had stationed his whole cavalry and all his archers and slingers opposite the enemy on the left wing.

89: Caesar, observing his previous custom, had posted his Tenth Legion on the right wing, and his Ninth on the left, though it had been seriously attenuated by the Dyrrachian battles. To this legion he added the Eighth, so that he almost made the two into one, having given orders that the one should support the other. He had eighty cohorts posted in his lines, making a total of twenty-two thousand men; two cohorts he had left as a protection for the camp. He had placed Antonius in command on the left wing, P. Sulla on the right, and Cn. Domitius in the centre. He himself confronted Pompeius. At the same time, having noticed the arrangements mentioned above, fearing lest his right wing should be surrounded by the multitude of cavalry, he hastily withdrew individual cohorts from the third line (ex tertia acie singulas cohortes detraxit) and out of these constructed a fourth line, stationing it opposite the cavalry, explaining what his object was and reminding them that the day's victory depended on the valour of these cohorts. At the same time he commanded the third line and the whole army not to join battle without orders from himself, saying that when he wished this to be done he would give the signal with a vexillum.

90: When, according to the custom of war, he was exhorting his army to battle, and setting forth his unbroken record of kindness to his men, he particularly reminded them that he could call his troops to witness with what zeal he had sought peace, what negotiations he had conducted through Vatinius in conferences and through Aulus Clodius with Scipio, how at Oricum he had urged Libo about the sending of envoys. He had never, he said, wished to squander the blood of his soldiers or to deprive the republic of either of its armies. After delivering this speech, the soldiers clamouring for action and burning with zeal for the fight, he gave the signal with a trumpet (tuba).

91: There was in Caesar's army an evocatus, C. Crastinus, who in the previous year had served under him as first centurion in the Tenth Legion, a man of remarkable valour. On the signal being given: "Follow me," said he, you who have been my comrades (manipulares), and give your inmperator your wonted loyal service. This one battle alone remains; when it is over he will recover his dignity and we our liberty." At the same time, looking at Caesar, he says: "To-day, General, I will give you occasion to thank me alive or dead." Having said this, he ran forward first from the right wing, and about one hundred and twenty picked men of the same cohort, serving as volunteers, followed him.

92: Between the two lines there was only as much space left as was necessary for the charge of each army. But Pompeius had previously ordered his men to await Caesar's attack without moving from their position, and to allow his line to fall into disorder. He is said to have done this on the advice of C. Triarius, in order that the first charge and impetus of the troops might be broken and their line spread out, and that so the Pompeians marshalled in their proper ranks might attack a scattered foe. He hoped, too, that the pila would fall with less effect if the men were kept in their place than if they themselves discharged their missiles (telis) and advanced; also that by having a double distance to run Caesar's soldiers would be breathless and overdone with fatigue. Now this seems to us to have been an irrational act on the part of Pompeius, because there is a certain keenness of spirit and impetuosity implanted by nature in all men which is kindled by the ardour of battle. This feeling it is the duty of commanders not to repress but to foster, nor was it without good reason that the custom was instituted of old that signals should sound in every direction and the whole body of men raise a shout, by which means they thought that the enemy were terrified and their own men stimulated.

93: But when our men on the giving of the signal, had run forward with javelins levelled (cum infestus pilis) and had observed that the Pompeians were not advancing against them, profiting by the experience they had gained in former battles, they spontaneously checked their speed and halted in about the middle of the space, so that they might not approach the foe with their vigour exhausted; and after a brief interval, again renewing their rapid advance, they discharged their pila and quickly drew their swords, according to Caesar's directions. Nor indeed did the Pompeians fail to meet the emergency. For they parried the shower of missiles (tela) and withstood the attack of the legions without breaking their ranks, and after discharging their javelins (pilis) had recourse to their swords. At the same time the horse on Pompeius' left wing, according to orders, charged in a body, and the whole multitude of archers poured forth. Our cavalry, failing to withstand their attack, gradually quitted their position and retired. Pompeius' cavalry pressed forward all the more eagerly, and deploying by squadrons began to surround our lines on their exposed flank. Caesar, observing it, gave the signal to his fourth line, which he had composed of six cohorts (quam instituerat sex cohortium; but the texts actually have "ex cohortium numero"). These advanced rapidly and with colours flying (infestisque signis)  attacked Pompeius' horse with such fury that not one of them stood his ground, and all, wheeling round, not only quitted the position but forthwith in hurried flight made for the highest hills. When these were dislodged all the archers and slingers, left defenceless, without support, were slain. With the same onslaught the cohorts surrounded the left wing, the Pompeians still fighting and continuing their resistance in their lines, and attacked them in the rear.

94: At the same time Caesar ordered the third line, which had been undisturbed and up to that time had retained its position, to advance. So, as they had come up fresh and vigorous in place of the exhausted troops, while others were attacking in the rear, the Pompeians could not hold their ground and turned to flight in mass. Nor was Caesar wrong in thinking that the victory would originate with those cohorts which had been posted opposite the cavalry in the fourth line, as he had himself stated in exhorting his troops; for it was by them that the cavalry was first repulsed, by them that the archers and slingers were slaughtered, by them that the Pompeian force was surrounded on the left and the rout first started. But Pompeius, when he saw his cavalry beaten back and that part of his force in which he had most confidence panic-stricken, mistrusting the rest also, left the field and straightway rode off to the camp. To the centurions whom he had placed on duty at the praetorian gate he exclaimed in a loud voice that the troops might hear: "Protect the camp and defend it carefully if anything goes amiss. I am going round the other gates and encouraging the guards of the camp." Having said this, he betook himself to the general's headquarters, mistrusting his fortunes and yet waiting to see the issue.

95: When the Pompeians were driven in flight within the rampart, Caesar, thinking that no respite should be given them in their terror, urged his men to take advantage of the kindness of fortune and attack the camp. And though fatigued by the great heat, for the action had been prolonged till noon, they nevertheless obeyed his command, with a spirit ready for every toil. The camp was being zealously defended by the cohorts which had been left there on guard, and much more keenly still by the Thracians and barbarian auxiliaries (a Thracibus barbarisque auxiliis). For the soldiers who had fled from the battlefield panic-stricken in spirit and exhausted by fatigue, many of them having thrown away their arms and their military standards, were thinking more of further flight than of the defence of the camp. Nor could those who had planted themselves on the rampart stand up any longer against the multitude of javelins (telorum), but, worn out by wounds, quitted their position, and forthwith all, following the guidance of centurions and military tribunes, fled for refuge to some very lofty hills that stretched up to the camp.

96: [...]  When our men were now circulating within the rampart, Pompeius, procuring a horse and tearing off his insignia as Imperator, flung himself out of the camp by the decuman gate and, putting spurs to his horse, hurried straight off to Larisa. Nor did he halt there, but, coming across a few of his men in flight, with undiminished speed, not stopping his course at night, arrives at the sea with a retinue of thirty horsemen and embarks on board a corn-ship [...]

97: Caesar having got possession of the camp urgently demands of his men not to let slip an opportunity of completing their task through absorption in plunder. Having gained his object, he begins to surround the hill with earthworks. The Pompeians, as the hill had no water supply, distrusting the position, began to withdraw in mass by its ridges towards Larisa. Caesar, observing this, divided his forces and ordered a part of the legions to remain in Pompeius' camp, and sent back part to his own camp; four legions he took with him and began to advance against the Pompeians by a more convenient route, and when he had proceeded four miles drew up his line. On observing this the Pompeians halted on a certain hill. The foot of this was washed by the river. Caesar exhorted his troops, and then, although they were worn out by the continuous toil of a whole day, and night was now coming on, nevertheless cut off the river from the hill by a line of fortification, so that the Pompeians might be unable to get water at night. When this work was concluded the enemy sent a deputation and began to treat of surrender. A few men of the senatorial order who had joined them sought safety in flight at nightfall.

98: At early dawn Caesar ordered all those who had taken up their position on the hill to come down from the higher ground to the plain and to throw down their arms. [...] 

99: In this battle he lost not more than two hundred from the ranks, but about thirty brave centurions. Also Crastinus, whom we have mentioned above, was slain by a sword-stroke in his face while fighting with the utmost bravery. Nor did the remark which he had made when starting out for the fight prove false, for Caesar was of opinion that the valour of Crastinus in that battle had been most remarkable, and judged that he had rendered him a great service. Of the Pompeian army about fifteen thousand appeared to have fallen, but more than twenty-four thousand surrendered, for even the cohorts which had been on garrison duty in the forts surrendered to Sulla; many besides fled to the neighbouring communities. There were brought to Caesar from the battle one hundred and eighty military standards and nine eagles. L. Domitius in his flight from the camp to the mountain was slain by the cavalry, his strength having failed him from fatigue.

Commentary
The numbers I have cited above are those given by Caesar, with no consideration of what other sources may say. Some give figures of c.30,000 Caesarean infantry, which might argue for 8,000 or so light infantry on top of his figure of 22,000 legionaries; but other explanations are possible. Delbruck's argument for c.32,000 legionaries alone can be found here.

There is some uncertainty in the text about the strength of Caesar's fourth line; the surviving text of Caesar does not give a number of cohorts, but it is explicitly given as six cohorts in other accounts. The text of the Civil War is usually restored to give that meaning, by changing "ex cohortium" to "sex cohortium" – see the discussion in more detail at http://soa.org.uk/sm/index.php?topic=1729.msg19623#msg19623

Available secondary articles
Modern accounts and analyses of Pharsalus are numerous; among them, the following modern(-ish) articles easily available on the web may be interesting:

•   B Perrin, "The Crastinus episode at Palaepharsalus", Transactions of the American Philological Association 15 (1884); free JSTOR download from http://www.jstor.org/stable/2935799   

•   B Perrin, "Pharsalia, Pharsalus, Palaepharsalus", The American Journal of Philology Vol. 6, No. 2 (1885); free JSTOR download from http://www.jstor.org/stable/287135

•   Arthur Searle, "Note on the Battle of Pharsalus", Harvard Studies in Classical Philology 18 (1907); free JSTOR download from http://www.jstor.org/stable/310555

•   T Rice Holmes, "The Battle-field of Old Pharsalus", The Classical Quarterly  Vol. 2 (1908); online at http://penelope.uchicago.edu/Thayer/E/Journals/CQ/2/4/Battlefield_of_Old_Pharsalus*.html

•   J P Postgate, "The Site of the Battle of Pharsalia", Journal of Roman Studies Vol. 12 (1922); online at http://penelope.uchicago.edu/Thayer/E/Journals/JRS/12/Site_of_Pharsalia*.html

•   William E. Gwatkin, Jr, "Some Reflections on the Battle of Pharsalus", Transactions of the American Philological Association 97 (1956); online at http://penelope.uchicago.edu/Thayer/E/Journals/TAPA/87/Pharsalus*.html

Couple of things which struck me on re-reading

1)     But in the case of his cavalry he retained his previous custom which we have explained above: since they were many times inferior in number, he gave orders that lightly equipped youths from among the first-rank men (adulescentes atque expeditos ex antesignanis), with arms selected with a view to fleetness (electis ad pernicitatem armis), should go into battle among the cavalry, so that by daily practice they might win experience in this kind of fighting also.

So these men were also drawn from the legions? In which case there might have been two cohorts 'equivalent' of these

2) Reading 88 where Pompey draws up his army. Both sides seem to have put their best legions on the open flank, and the rest of the line (with both armies) doesn't seem to be numbered legions but 'Cohorts'
Now it's possible that Caesar had forgotten the legions on his own side but that strikes me as unlikely. Was it that a lot of the newly raised legions deployed on both sides, perhaps especially Pompey's, were legions in name only, and that men had been raised as cohorts and the cohorts brought together as legions, and the legions were still unsure of themselves and their identity?

3) To sort of support this point, once his 'named' legions go down, Pompey abandons the field, the others might not have had the cohesion to cope with a setback and he knew it.

Jim

Quote from: Jim Webster on May 24, 2015, 06:42:52 PM
Couple of things which struck me on re-reading

1)     But in the case of his cavalry he retained his previous custom which we have explained above: since they were many times inferior in number, he gave orders that lightly equipped youths from among the first-rank men (adulescentes atque expeditos ex antesignanis), with arms selected with a view to fleetness (electis ad pernicitatem armis), should go into battle among the cavalry, so that by daily practice they might win experience in this kind of fighting also.

So these men were also drawn from the legions? In which case there might have been two cohorts 'equivalent' of these

An uncertain number of Caesar's cavalry - 400 of his 1,000? - were his Germans. Would they have had their own supporting infantry with them already? If so he'd have needed to withdraw fewer men from the legions.

Tricky one.
Is Caesar upgrading the others to give them the advantage the Germans obviously had, or is it as much digging back into history to recover a tactic that worked well in the past. Or is it one, but sold as the other 

If the Germans had their own infantry with them, then they would technically come from the light infantry pool but as we haven't got a clue how many there were of them, a few hundred Germans is neither here nor there.

But I suppose there's at least a strong cohort's worth of infantry drawn from the legions to add to the cavalry.

But I've been pondering the cohorts where legions aren't mentioned. Is this an artifact of our sources or is it a case that these were raised as cohorts, at some point amalgamated into legion but due to lack of time to build espirit d'corps, the legions had remained nominal. If so you could imagine that it would weaken the line, because cohorts in the second rank might not feel the same obligation to push forward to support the cohorts in the front rank. (for example)

It might make the 'legions' a bit more brittle than we'd otherwise expect

Jim

Quote from: Jim Webster on May 26, 2015, 10:27:31 AMBut I've been pondering the cohorts where legions aren't mentioned. Is this an artifact of our sources or is it a case that these were raised as cohorts, at some point amalgamated into legion but due to lack of time to build espirit d'corps, the legions had remained nominal. If so you could imagine that it would weaken the line, because cohorts in the second rank might not feel the same obligation to push forward to support the cohorts in the front rank. (for example)

It might make the 'legions' a bit more brittle than we'd otherwise expect

We do have Caesar speaking, for example, of 22 cohorts being raised in Cisalpine Gaul (BG VII.65), and the very likely suggestion has been made that it was these very cohorts (or some of them) who became Legio V Alauda; so yes, substantial forces were sometimes raised as "so many cohorts"; but in this case. the legion they eventually became was not noted for fragility.

Quote from: Jim Webster on May 26, 2015, 10:27:31 AM

But I've been pondering the cohorts where legions aren't mentioned. Is this an artifact of our sources or is it a case that these were raised as cohorts, at some point amalgamated into legion but due to lack of time to build espirit d'corps, the legions had remained nominal.

In addition the detail Duncan has mentioned, it would seem that in this period troops were raised as cohorts (cf.Civil War I.15, in which Vibullius Rufus "then proceeded to muster what cohorts he could from the levies ordered by Pompey" and Domitius "raised about twenty cohorts from Alba, the Marsi, the Paeligni and the surrounding districts".

Such cohorts might or might not subsequently be incorporated into legions: Domitius, besieged in Corfinium, wrote to Pompey to say that if not relieved, "he himself and more than thirty cohorts" would be in danger.  Not, we note three legions: I suspect that turning collections of cohorts into legions was the prerogative of the Senatus Populusque Romanus or a consul acting in their name, or even a provinical governor with authority - just minting an eagle and dropping it into the hands of a signifer would not be sufficient: there would also be tribunes and legates to be appointed, ceremonies undertaken and so on and so forth.

Anyone with good knowledge of Roman legal procedure might be able to give a better picture of what was involved in turning a collection of cohorts into actual legions.

Pompey's recruiting officers raised several legions in the east - these seem to have been proper legions in every respect except troop quality, being recently raised from basically unpromising material.  Caesar also had the odd freshly-raised legion,  but seems to have put such troops on garrison duty or detached service: in III.34 he reassembles a legion which had been guarding the coast sends Lucius Cassius Longinus with the newly-raised XXVII Legion and 200 cavalry into Thessaly, although he omits mention of how he fared: we learn from Cassius Dio (XLI.51.2) that Longinus was "disastrously defeated in Thessaly by Scipio and by Sadalus, a Thracian" - Calvinus, with the experienced XI and XII Legions, had done somewhat better, overcoming his opponent in a battle but having to draw off when Pompey's main force arrived (cf. Civil War III.36, which glosses over the reverse suffered by Longinus).

In Italy, Caesar often detaches cohorts from his existing legions to secure territory or to undertake a specific task, e.g. in I.12 Caesar sends Curio with three cohorts from Pisaurum and Ariminium to tackle five cohorts under Thermus at Iguvium.  The three cohorts appear to have been from the XIII Legion at Arimunium, and hence had the advantage of having served together and probably having stood in the same line of battle.  None of Thermus' five recently-raised cohorts had seen service or acted together, and Thermus declined to put matters to the test: he fled and his troops deserted and went home, which underlies that Pompey's levy and cause were not universally popular.

Source Ia:
Caesar, Civil War, III.4

This passage from earlier in Caesar's account, describing Pompey's army before the battles at Dyrrachium, throws more light on the composition of his light infantry and particularly his cavalry:

4: [Pompeius] had made up nine legions of Roman citizens: five from Italy, which he had conveyed across the sea; one of veterans from Cilicia, which, being formed out of two legions, he called Gemella ["the Twin Legion"]; one from Crete and Macedonia out of veteran troops which, when disbanded by their former commanders, had settled in those provinces; two from Asia, for the levying of which the consul Lentulus had arranged. Besides, he had distributed among the legions by way of supplement a large number of men from Thessaly, Boeotia, Achaia, and Epirus. With these he had mixed men who had served under Antonius. Besides these he was expecting two legions with Scipio from Syria. He had archers from Crete and Lacedaemon, from Pontus and Syria and the other states, to the number of three thousand; also two 600-strong cohorts of slingers, and seven thousand horsemen. Of these Deiotarus had brought six hundred Gauls, and Ariobarzanes five hundred from Cappadocia; Cotys had provided the same number from Thrace and had sent his son Sadalas; from Macedonia there were two hundred under the command of Rhascupolis, a man of marked valour. The young Pompeius had brought with his fleet five hundred of the Gabinian troops from Alexandria, Gauls and Germans, whom A. Gabinius had left there with King Ptolemy on garrison duty. He had collected eight hundred from his own slaves and from his list of herdsmen [ex servis suis pastorumque suorum numero]. Tarcondarius Castor and Domnilaus had provided three hundred from Gallograecia; of these the one had come with his men, the other had sent his son. From Syria two hundred had been sent by Antiochus of Commagene, on whom Pompeius bestowed large rewards, and among them many mounted archers. To these Pompeius had added Dardani and Bessi, partly mercenaries, partly secured by his authority or influence, also Macedonians, Thessalians, and men of other nations and states, and had thus filled up the number stated above.

Commentary

I think this is the most detailed list of Pompey's cavalry that we have, and even so the enumerated contingents only add up to 3,600 of his supposed total of 7,000. Appian's list of auxiliaries (Civil Wars II.71) adds some other nationalities without specifying whether they provided infantry or cavalry; nations such as the Armenians may perhaps account for some of the "missing" cavalry. So may the contingent of young Roman aristocrats implied in some accounts.

Deiotarus' "Galli" and Tarcondarius Castor's "Gallograeci" are both Galatians from Asia Minor, presumably not yet completely united despite the Senate having given Deiotarus the title of King. I wonder if Pompey's "slaves and herdsmen" might be a derogatory way of referring to his "clients" in general. Neither the Dardani nor the Bessi are famous as horsemen, the Bessi being best known for providing fierce mountain infantry, so  these may be additions to the list of Pompey's auxiliaries in general rather than specifically to his cavalry. (Caesar at III.95 mentions Thracians among Pompey's camp-guard at  Pharsalus, so that may perhaps be where these Thracian Bessi ended up).

Edit: There is an article on auxiliary troops in the late Republic at http://www.sfb600.uni-trier.de/filebase/A2/yoshimura.pdf which might be useful; it contains a list of princes said in various sources to have assisted Pompey.

I have come to believe that the troops raised at the beginning of the civil war between Caesar and Pompey were hastily raised by cohorts not unlike regiments raised at the beginning of the American Civil War. The cohorts were rapidly raised and quickly sent to join their respective generals. Due to the circumstances, I doubt there was time to organize, train, and officially create legions from those cohorts.

As far as the legality of raising a legion, that's probably a gray area in Roman law. When Caesar became governor of Cisalpine Gaul and Illyricum he would have been invested by the Senate with imperium, the right to command troops, and auspicia, the right to consult the gods. These powers are granted to any governor to allow them to act on behalf of the state and the Senate. These powers probably gave some authority to Caesar to raise lesions as he did when he raised two new legions to face the Helvetii. I do remember reading somewhere that raising the two new lesions may have exceeded Caesar's authority as governor. But, I don't remember reading anywhere that the Senate ordered Caesar to disband his newly raise legions. He probably would ignored the order anyway and found some justification for his actions.

As far as raising legions and troops during the Civil War, Caesar been declared an outlaw and his legal powers revoked by the Senate. There again, I doubt that Caesar would've let the little problem of being declared an outlaw stand in the way of his raising and designating legions as he needed. After all, the die had been cast.

That's why I think the raising of independent cohorts was a matter of practicality rather than legality.

Source 2
Appian, The Civil Wars

II, 49: On the two commanders' forces, before the Dyrrachium fighting:
Caesar at that time had ten legions of infantry and 10,000 Keltic horse [Kelton hippeis murioi]. Pompey had five legions from Italy, with which he had crossed the Adriatic, and the cavalry belonging to them; also the two surviving legions that had served with Crassus in the Parthian war ... and a certain part of those who had made the incursion into Egypt with Gabinius, making altogether eleven legions of Italian troops and about 7000 horse. He had allies also from Ionia, Macedonia, Peloponnesus, and Boeotia, Cretan archers, Thracian slingers, and Pontic javelin-throwers. He had also some Keltic horse and others from eastern Galatia, together with Commageneans sent by Antiochus, Cilicians, Cappadocians, some from Lesser Armenia, and Pamphylians and Pisidians. Pompey did not intend to use all these for fighting. Some were employed in garrison duty, in building fortifications, and in other service for the Italian soldiers, so that none of the latter should be kept away from the battles. Such were Pompey's land forces.

II, 70-82: The Battle of Pharsalus
70: Since many writers differ as to Caesar's army, I shall follow the most credible Roman authorities, who give the most careful enumeration of the Italian soldiers, as the backbone of the army, but do not make much account of the allied forces or record them exactly, regarding them as mere foreigners and as contributing little to the issue of the day. The army, then, consisted of about 22,000 men and of these about 1000 were cavalry. Pompey had more than double that number, of whom about 7000 were cavalry. Some of the most trustworthy writers say that 70,000 Italian soldiers were engaged in this battle. Others give the smaller number, 60,000. Still others, grossly exaggerating, say 400,000. Of the whole number some say Pompey's forces were half as many again as Caesar's, others that they were two-thirds of the total number engaged. So much doubt is there as to the exact truth. However that may be, each of them placed his chief reliance on his Italian troops. In the way of allied forces Caesar had cavalry from both Cisalpine and Transalpine Gaul, besides some light-armed Greeks ('Ellēnōn d'epeltazōn), consisting of Dolopians, Acarnanians, and Aetolians. Such were Caesar's allies. Pompey had a great number from all the eastern nations, part horse, part foot. From Greece he had Lacedaemonians marshalled by their own kings, and others from Peloponnesus and Boeotians with them. Athenians marched to his aid also, although proclamation had been made that they, being consecrated to the Thesmophoroi, should do no harm to the army of either party. Nevertheless, they wished to share in the glory of the war because this was a contest for the Roman leadership.

71: Besides the Greeks almost all the nations in the circle of the eastern sea sent aid to Pompey: Thracians and Hellespontines and Bithynians and Phrygians and Ionians, Lydians and Pamphylians and Pisidians and Paphlagonians, and Cilicia, Syria, Phoenicia, the nation of the Hebrews, and their neighbours the Arabs; Cyprians and Rhodians and Cretan slingers [or "and Rhodian and Cretan slingers": "... te kai Rhodioi kai Krētes sphendonētai"], and all the other islanders. Kings and princes were there leading their own troops: Deïotarus, the tetrarch of Galatia, and Ariarathes, king of Cappadocia. Taxiles commanded the Armenians from the hither side of the Euphrates; those from the other side were led by Megabates, the lieutenant of King Artapates. Some other small princes took part with Pompey in the action. It was said that sixty ships from Egypt were contributed to him by the sovereigns of that country, Cleopatra and her brother, who was still a boy. But these did not take part in the battle, nor did any other naval force, but they remained idle at Corcyra. Pompey seems to have acted very foolishly in this respect both in disregarding the fleet, in which he excelled so greatly that he could have deprived the enemy of all the supplies brought to them from abroad, and in risking a battle on land with men exulting in their recent labours, and thirsting like tigers for blood. Although he had been on his guard against them at Dyrrachium, a certain spell seems to have come over him, most opportunely for Caesar, with the result that Pompey's army became light-headed to a degree, taking entire charge of its commander, and rushing into action in a most unworkmanlike way.

72: [Pompey's speech]

73: [Caesar's speech]

74: [continued] "Nor is it difficult for hardy and veteran soldiers to overcome new recruits who are without experience in war, and who, moreover, like boys, spurn the rules of discipline and of obedience to their commander. ... I say these things of his Italian forces only. As for his allies, do not think about them, pay no attention to them, do not fight with them at all. They are Syrian, Phrygian, and Lydian slaves, always ready for flight or servitude. I know very well, and you will presently see, that Pompey himself will not entrust to them any place in the ranks of war. Give your attention to the Italians only, even though those allies come running around you like dogs trying to frighten you. When you have put the enemy to flight let us spare the Italians as being our own kindred, but slaughter the allies in order to strike terror into the others. Before all else, in order that I may know that you are mindful of your promise to choose victory or death, throw down the walls of your camp as you go out to battle and fill up the ditch, so that we may have no place of refuge if we do not conquer, and so that the enemy may see that we have no camp and know that we are compelled to encamp in theirs."

75: Nevertheless, after he had thus spoken Caesar detailed 2,000 of his oldest men to guard the tents. The rest, as they passed out, demolished their fortification in the profoundest silence and filled up the ditch with the debris. When Pompey saw this, although some of his friends thought that it was a preparation for flight, he knew it was an exhibition of daring, and groaned in spirit, to think that they were now coming to grips with wild beasts although they had on their side famine, the best tamer of wild beasts. But there was no drawing back now, when things were balanced on the razor's edge. Wherefore, leaving 4,000 of his Italian troops to guard his camp, Pompey drew up the remainder between the city of Pharsalus and the river Enipeus opposite the place where Caesar was marshalling his forces. Each of them ranged his Italians in front, divided into three lines with a moderate space between them, and placed his cavalry on the wings of each division. Archers and slingers were mingled among all. Thus were the Italian troops disposed, on which each commander placed his chief reliance. The allied forces were marshalled by themselves rather for show than for use. There was much jargon and confusion of tongues among Pompey's auxiliaries. Pompey stationed the Macedonians, Peloponnesians, Boeotians, and Athenians near the Italian legions, as he approved of their good order and quiet behaviour. The rest, as Caesar had anticipated, he ordered to lie in wait by tribes outside of the line of battle, and when the engagement should become close to surround the enemy, to pursue, to do what damage they could, and to plunder Caesar's camp, which was without defences.

76: The centre of Pompey's formation was commanded by his father-in‑law, Scipio, the left wing by Domitius, and the right by Lentulus. Afranius and Pompey guarded the camp. On Caesar's side the commanders were Sulla, Antony, and Domitius. Caesar took his place in the tenth legion, on the right wing, as was his custom. When the enemy saw this they transferred, to face that legion, the best of their horse, in order to surround it if they could, by their superiority of numbers. When Caesar perceived this movement he placed 3,000 of his bravest foot-soldiers in ambush and ordered them, when they should see the enemy trying to flank him, to rise, dart forward, and thrust their spears directly in the faces of the men because, as they were fresh and inexperienced and still in the bloom of youth, they would not endure injury to their faces. Thus they laid their plans against each other, and each commander passed through the ranks of his own troops, attending to what was needful, exhorting his men to courage, and giving them the watchword, which on Caesar's side was "Venus the Victorious," and on Pompey's "Hercules the Invincible."

77: When all was in readiness on both sides they waited for some time in profound silence, hesitating, looking steadfastly at each other, each expecting the other to begin the battle. [...]

78: When they were waiting and looking at each other the day was advancing. All the Italian troops stood motionless in their places, but when Pompey saw that his allied forces were falling into confusion by reason of the delay he feared lest the disorder should spread from them before the beginning of the battle. So he sounded the signal first and Caesar echoed it back. Straightway the trumpets, of which there were many distributed among the divisions of so great a host, aroused the soldiers with their inspiring blasts, and the standard-bearers and officers put themselves in motion and exhorted their men. They all advanced confidently to the encounter, but with stupor and the deepest silence, like men who had had experience in many similar engagements. And now, as they came nearer together, there was first a discharge of arrows and stones. Then, as the cavalry were a little in advance of the infantry, they charged each other. Those of Pompey prevailed and began to outflank the tenth legion. Caesar then gave the signal to the cohorts in ambush and these, starting up suddenly, advanced to meet the cavalry, and with spears (tois dorasin) elevated aimed at the faces of the riders, who could not endure the enemy's savagery, nor the blows on their mouths and eyes, but fled in disorder. Thereupon Caesar's men, who had just now been afraid of being surrounded, fell upon the flank of Pompey's infantry which was denuded of its cavalry supports.

79: When Pompey learned this he ordered his infantry not to advance farther, not to break the line of formation, and not to hurl the javelin, but to open their ranks, bring their spears to rest, and so ward off the onset of the enemy. Some persons praise this order of Pompey as the best in a case where one is attacked in flank, but Caesar criticises it in his letters. He says that the blows are delivered with more force, and that the spirits of the men are raised, by running, while those who stand still lose courage by reason of their immobility and become excellent targets for those charging against them. So, he says, it proved in this case, for the tenth legion, with Caesar himself, surrounded Pompey's left wing, now deprived of cavalry, and assailed it with javelins in flank, where it stood immovable; until, finally, the assailants threw it into disorder, routed it, and this was the beginning of the victory. In the rest of the field slaughter and wounding of all kinds were going on, but no cry came from the scene of carnage, no lamentation from the wounded or the dying, only sighs and groans from those who were falling honourably in their tracks. The allies, who were looking at the battle as at a spectacle, were astonished at the discipline of the combatants. So dumbfounded were they that they did not dare attack Caesar's tents, although they were guarded only by a few old men. Nor did they accomplish anything else, but stood in a kind of stupor.

80: As Pompey's left wing began to give way his men even still retired step by step and in perfect order, but the allies who had not been in the fight, fled with headlong speed, shouting, "We are vanquished," dashed upon their own tents and fortifications as though they had been the enemy's, and pulled down and plundered whatever they could carry away in their flight. Then the rest of Pompey's Italian legions, perceiving the disaster to the left wing, retired slowly at first, in good order, and still resisting as well as they could; but when the enemy, flushed with victory, pressed upon them they turned in flight. Thereupon Caesar, in order that they might not rally, and that this might be the end of the whole war and not of one battle merely, with greater prudence than he had ever shown before, sent heralds everywhere among the ranks to order the victors to spare their own countrymen and to smite only the auxiliaries. The heralds drew near to the retreating enemy and told them to stand still and fear not. As this proclamation was passed from man to man they halted, and the phrase "stand and fear not" began to be passed as a sort of watchword among Pompey's soldiers; for, being Italians, they were clad in the same style as Caesar's men and spoke the same language. Accordingly, the latter passed by them and fell upon the auxiliaries, who were not able to resist, and made a very great slaughter among them.

81: When Pompey saw the retreat of his men he became bereft of his senses and retired at a slow pace to his camp, and when he reached his tent he sat down speechless, resembling Ajax, the son of Telamon, who, they say, suffered in like manner in the midst of his enemies at Troy, being deprived of his senses by some god. Very few of the rest returned to the camp, for Caesar's proclamation caused them to remain unharmed, and as their enemies had passed beyond them they dispersed in groups. As the day was declining Caesar ran hither and thither among his troops and besought them to continue their exertions till they should capture Pompey's camp, telling them that if they allowed the enemy to rally they would be the victors for only a single day, whereas if they should take the enemy's camp they would finish the war with this one blow. He stretched out his hands to them and took the lead in person. Although they were weary in body, the words and example of their commander lightened their spirits. Their success so far, and the hope of capturing the enemy's camp and its contents, excited them; for in the midst of hope and prosperity men feel fatigue least. So they fell upon the camp and assaulted it with the utmost disdain for the defenders. When Pompey learned this he started up from his strange silence, exclaiming, "What! in our very camp?" Having spoken thus he changed his clothing, mounted a horse, and fled with four friends, and did not draw rein until he reached Larissa early the next morning. So Caesar established himself in Pompey's camp as he had promised to do when he was preparing for the battle, and ate Pompey's supper, and the whole army feasted at the enemy's expense.

82: The losses of Italians on each side — for there was no report of the losses of auxiliaries, either because of their multitude or because they were despised — were as follows: in Caesar's army, thirty centurions and 200 legionaries, or, as some authorities have it, 1200; on Pompey's side ten senators, among whom was Lucius Domitius, the same who had been sent to succeed Caesar himself in Gaul, and about forty distinguished knights. Some exaggerating writers put the loss in the remainder of his forces at 25,000, but Asinius Pollio, who was one of Caesar's officers in this battle, records the number of dead Pompeians found as 6000.

Such was the result of the famous battle of Pharsalus. Caesar himself carries off the palm for first and second place by common consent, and with him the tenth legion. The third place is taken by the centurion Crassinius, whom Caesar asked at the beginning of the battle what result he anticipated, and who responded proudly, "We shall conquer, O Caesar, and you will thank me either living or dead." The whole army testifies that he darted through the ranks like one possessed and did many brilliant deeds. When sought for he was found among the dead, and Caesar bestowed military honours on his body and buried it, and erected a special tomb for him near the common burial-place of the others.

Commentary
Appian looks to have used Caesar's own account as a source, since the 22,000 Caesarians of II.70 match Caesar's own figures, and the suggestion that Pompey had twice as many men matches Caesar's figure of 45,000 Pompeians. Appian does seem to have misread Caesar when he suggests that the 1,000 Caesarian horse were included in the figure of 22,000; Caesar says they are additional. (The 10,000 Gallic cavalry of II.49 must be a simple mistake.)

However Appian clearly had other sources as well, who give him the divergent troop numbers he mentions, some quite close to Caesar's figures, but at least one exaggerating to almost Herodotean proportions. At II.82 he mentions one such source, Asinius Pollio.

Appian identifies Caesar's light infantry - "'Ellēnōn d'epeltazōn", "of Greeks serving as peltasts" - though without giving us a number for them, whereas Caesar sees no need to list any such auxiliaries. They were western Greeks, probably recruited locally during the Dyrrachium phase of the campaign or on the march into Thessaly.

Appian's information on Pompey's auxiliaries more or less matches up to what Caesar tells us, though he adds some more nationalities, such as the Armenians. Pompey's "Cretan slingers" at II.71 are a bit of a surprise, but since II.49 gives the more expected Cretan archers (as indeed does Caesar III.4), it seems more likely that Appian's text (or his source) originally listed Rhodian slingers and Cretan archers. (At II.49 he has Thracian slingers, but since Caesar tells us that Pompey had two cohorts of slingers, that need not be a problem.)

Note that Appian gives numbers of men in some cases where Caesar gives numbers of cohorts: Caesar's two-cohort camp-guard becomes 2,000 men; Pompey's seven cohorts become 4,000; Caesar's six(?) cohorts of the fourth line become 3,000 men. We do not know where Appian got these numbers, but clearly he 's not just using a simple multiplier of x men per cohort.

Appian's account of the course of the battle broadly follows Caesar's. He gives the credit for the initial outflanking of the Pompeian line to the Tenth legion, where Caesar himself lays more stress on the fourth line turning on the infantry after defeating the cavalry.

Duncan, thanks for the tip on Appian.

Have you ever run across any details on the eastern forces at Pharsalus? I presume the "Syrian legions" were the troops who survived Carrhae mentioned by Dio in Roman History 40.27 and I see the wiki entry on Syria (Roman province) states three legions.

Specifically, anyone have any idea what type of "Hebrew" forces were at Pharsalus?

I don't recall any information on the Eastern auxiliaries that isn't in Caesar or Appian - except that Lucan in the Pharsalia mentions Arab, Mede and Ituraean archers in Pompey's army. The auxiliaries whom Appian calls to Hebraion genos - which is a bit unusual, I think, Ioudaioi is more common - were presumably from the Kingdom of Judaea, which was then ruled by Antipater (Herod the Great's father) as a client of Pompey. Not long after Pharsalus, he shifted his allegiance to Caesar and contributed 3,000 infantry called hoplitai by Josephus to Mithridates of Pergamon's army that rescued Caesar in Egypt. Given that Alexander Jannaeus' "hundred-killers" fighting Ptolemy Lathyrus about 100 BC are said (again by Josephus) to have bronze-faced thyreoi - and this is the chronologically closest description of Judaean military equipment that I know of - then I reckon the Jewish infantry at Pharsalus are most likely to have been either thyreophoroi or, perhaps less likely, "armed in Roman style".

Not read it yet myself (this week has been manic  ) but Steven James has done something on Pharsalus

https://independent.academia.edu/StevenJames1   

Steven is as usual interesting and innovative, but a bit too formulaic for my tastes.  For example,

Quote
Caesar's auxiliary infantry are listed as being Dolopians, Acarnanians, and Aetolians. With the ratio of
legionaries to auxiliary infantry at 3:1, Caesar's 27,000 legionaries would be accompanied by 9,000 auxiliary infantry.

I don't think that Steven demonstrates in this paper that 1 auxiliary to 3 legionaries was a standard figure at this period; I assume he has done so elsewhere. Even if that is the case, he seems to be taking for granted that actual armies always follow standard regulations. If the Aitolians (etc) had turned up with 10,000 auxiliary infantry, do we think Caesar would have turned some of them away? If on the other hand those states had not offered as many men as were required for the "standard" proportion, how would we know?

Quote
Therefore, Caesar's seven legions at full strength were assigned 1,200 auxiliary infantry (600 archers and 600 slingers)

I don't think the suggestion that these auxiliaries were archers and slingers fits very well with the verb Appian uses - "epeltazōn", literally "being with peltai", or "being peltasts". It's true that Appian does say that:

QuoteArchers and slingers were mingled among all.

implying that both sides had such psiloi mixed with their legionaries; but this is explicitly contradicted by Caesar's statement that Pompey had "all his archers and slingers" with the cavalry "on the left wing", so not much weight can be given to it.

However, there are some useful thoughts in there about the legionary strengths. And Steven also raises a real issue about Pompey's cavalry numbers: Caesar says he had 7,000, but only lists 3,600. I've suggested above that perhaps some of the other nationalities listed by Appian may have provided cavalrymen not included in Caesar's list. Steven suggests that perhaps:

Quotethe missing 3,000 cavalrymen are part of the 5,000 auxiliary infantry that are reported to be stationed behind the cavalry

If he's saying that some of the "cavalry" were in fact serving as infantry, then that sort of fits with another possibility I've been thinking about - that perhaps Caesar simply exaggerated the number of Pompey's horsemen?

Quote from: Duncan Head on December 28, 2015, 11:09:14 PM
Steven is as usual interesting and innovative, but a bit too formulaic for my tastes. 

That puts it very nicely.  Steven is very methodical but seems to assume that Caesar's legions - apart from the IX, which he has at exactly half-strength - would all be at full theoretical TO&E strengths despite having campaigned across the length and breadth of Greece, suffered attrition at Dyrrhachium and generally been understrength when originally loaded to cross over into Greece.

Steven remains convinced that the authorised legion strength more or less from when legions were first invented was 3,600 legionary heavy infantry plus 1,200 integral skirmish types provided by allies - not just Italian allies, but also Numidians, Cretans etc.  Inconsistency with Polybius' or Livy's organisation does not seem to worry him, but the big problem with his proposed organisation is that it becomes very difficult to reconcile with recorded cohort strengths and the Roman order of battle.

Quote
Steven suggests that perhaps:

Quotethe missing 3,000 cavalrymen are part of the 5,000 auxiliary infantry that are reported to be stationed behind the cavalry

If he's saying that some of the "cavalry" were in fact serving as infantry, then that sort of fits with another possibility I've been thinking about - that perhaps Caesar simply exaggerated the number of Pompey's horsemen?

I have wondered about this, although if Caesar were consciously exaggerating, he might be expected to inflate the sizes of the contingents he does detail in order to arrive at his figure of 7,000 cavalry rather than leaving a large and suspicious blank.  One may note that he omits the foot auxiliaries recorded by Appian, which suggests that over-representing or even fully representing Pompey's forces was not necessarily on his mind. 

My own reading of Caeasar's partial arithmetic is that he has listed the Pompeian non-legionary cavalry - if Pompey had 300 cavalry integral to each legion as per tradition, the resultant 3,300 cavalry from 11 legions would pretty much make up the 3,400-trooper shortfall.

To be fair to Steve he has taken men from the IX to bring other legions up to strength. But the problem we have is that we're not sure how accurate the figures for army strength are. If ancient authors have given us their figures based on what they thought full strength units were, then if we use their figures we will discover that they produce full strength units.
We also have the issue of casualties before the battle. Writing afterwards Caesar had reason to exaggerate previous losses. First it would make his victory more glorious, both by shrinking the size of his army, and also exaggerating enemy losses on the field to his losses on the field.

Looking at the Cavalry, was there legionary cavalry in this period? Caesar doesn't appear to have had any otherwise with about 8 legions with 300 per legion that's 2,400 cavalry that doesn't get a mention

With the auxiliaries, I agree that I see no reason why an ally should send exactly enough to fit in with Roman formations. But looking at the way Steve has arranged things, it does leave both armies with a 'dump' to put in 'spare' auxiliaries who aren't needed within the formal formations.