Could the Persian Empire logistically support an army several million strong?

[Erpingham]

We'll Patrick, if you class the Marie Louise's as prime fighting men, it really says all there is to say about your opinions

To be fair to Patrick, his 10% does include a full 50% of support forces who clearly weren't thought of as prime fighting anything.

[Erpingham]

This is why the 1% full-time professional, 10% optimal and 20% maximum available manpower figures are taken from other, more recent, societies for which we do have reliable population records.  There would seem to be no good reason why these would not retrofit into previous civilisations.

How about a totally different social structure and level of technology?

I suspect our lack of solid figures will take us nowhere with this line of argument.  But, having had to look at comparative figures as part of the argument, using internet available examples, a working hypothesis that ancient empires could mobilise 1-2% of their population for war seems justified. 

Addendum : I've looked again at the Roman Republic figures, which, according to some, show much greater mobilisations.  Part of the problem is that Roman Republican figures are often quoted as % of citizens and that as a percentage of the population needs to be estimated.  Approximately  a third of Rome's population were slaves, presumably in higher than natural proportions of adults, which throws us off on the rules of thumb.  However, it can be said Rome often had 25% of male citizens under arms. This may be up to 4% of the total population.

It seems also we will have some problems in generally applying these percentages just using an Empire population estimate, because population densities of the individual parts varied but many of the representives of the outer reaches of the Empire only supplied symbolic contingents, not proportional to their manpower.  Overall, I think we have taken this as far as it can be stretched, which frankly isn't that far.

[Patrick Waterson]

  Where the idea emerged that 10% must be mustered every time, I do not know.

Could it be statements like

Where they take us is to the realisation that prime military manpower is generally accepted to be 10% of population. 

You seem to flip between a "generally accepted" rule and the idea it didn't apply every time.  In fact, from the example given, it applied once is over 200 years and that in the mature industrial age.

There is a difference between prime military manpower being available and being used.  It is always available; it will only be fully used if the person in charge a) sees a compelling need and b) has the authority and organisation to reach and retain everyone in that category (which was definitely not the case in many of the American instances, which are also complicated by a high rate of desertion).

The generally accepted rule is that 10% of your population is prime military manpower.  Another 10% is usable as military manpower but wil be challenged by anything more demanding than garrison work.  This does not mean that every time there is a fight everyone in these categories wil be called up - indeed, full mobilisation, especially for an expedition outside one's own borders, is likely to be the exception rather than the rule (as far as we know, the Achaemenids did it only once).

I think part of the problem is the concept of a super organised Persian state.  What evidence, other than the circular argument from Herodotus' figures, do we have for this?

There is a lot of evidence of Achaemenid bureaucracy lying around, whether hides in Egypt or clay tablets in Babylon.  We also have, for example, Diodorus' accounts of the attempts to reconquer Egypt, involving significant numbers (220,000 men and 600 triremes first time round; 330,000 men and 600 triremes the second time)and extensive preparations over more than one year.  This suggests a high level and degree of organisation.

This is why the 1% full-time professional, 10% optimal and 20% maximum available manpower figures are taken from other, more recent, societies for which we do have reliable population records.  There would seem to be no good reason why these would not retrofit into previous civilisations.

How about a totally different social structure and level of technology?

This would, if anything, work in favour of a higher mobilisation percentage because nobody is needed to man all the technology (factories, power stations, railways, etc.).

I suspect our lack of solid figures will take us nowhere with this line of argument.  But, having had to look at comparative figures as part of the argument, using internet available examples, a working hypothesis that ancient empires could mobilise 1-2% of their population for war seems justified.

That depends upon the empire.  What percentage of their population did Mongols mobilise, for example?  And how did the Romans run so short of manpower after Cannae as to be mobilising slaves if they only put around 2% of their men in their army?

Our friends in Livescience estimate that

"From the middle of the third to the end of the second centuries B.C., the adult male population was estimated to have risen from about 200,000 to 400,000 individuals."

A Roman census covered only adult males.  This would give a total population of 500,000 (c.250 BC) increasing to 1,000,000 (c.101 BC).  By 218 BC it might have been c.625,000 giving a prime manpower figure of 65,000.  4% of this population (625,000) is, incidentally, 25,000 men or the equivalent of five legions.

In 218 BC Rome loses the Battle of the Trebia and perhaps 8,000 legionaries (10,000 of 18,000 get away).  In 217 BC it loses at Trasimene with another c.15,000 killed or captured.  That is 23,000 out of the potential 65,000.  In 217 BC Fabius avoids any significant loss, but in 216 BC eight legions are committed - and lost - at Cannae, for about 30,000 further casualties (if Livy is right about 10,000 getting back to Rome one way or another).

Rome has thus lost the services of c.53,000 men in four years, exclusive of another perhaps 10,000 or so in another army wiped out by Gauls in 216 BC.  So of the prime military manpower with which Rome began 218 BC, it is now down to scrapings.  In theory there are only about 2,000 men left; in practice, four years worth of youngsters will have grown up to boost the total somewhat.  Rome is still desperately short of men, so it is no real surprise that unprecedented methods of recruitment are used to tap into the non-prime category to fill out the numbers.

What may be misleading is that Rome rarely if ever fielded its entire manpower at any one time: it instead decided upon the number of legions to be enrolled for a particular year and a particular purpose, the default being four legions divided between two consuls (which would be c.20,000 men or slightly under 4% of the population).  As the Second Punic War continued, this total rose to six, eight or even more in any given year - which blows the 4% figure (let alone 2%) out of the water; the eight legions at Cannae make it at least 8% and the other two in Gallia Cisalpina the same year bring it up to 10%.

I suspect our lack of solid figures will take us nowhere with this line of argument.

If you feel that point has been reached, we can call it a day.

[Patrick Waterson]

Which particular small space would that be?

Take your pick really.
I have no view on Xerxes' route.
Pick a bridge or a campsite or a valley they passed through, whatever you prefer.
I think it will be difficult to find any pre-modern example, let alone a pattern of examples, whereby so many soldiers, passed through such a small space in such a short period of time.
So it would be compelling if we could!

Let us take a bridge, specifically the bridge of boats Xerxes' army used to cross the Hellespont.  This is measurable because it was one trireme (or pentekonter) wide, and triremes and pentekonters had very similar dimensions, of which the important one is a length of c.120 feet.  This would be about the width of the bridge.  Screens were erected on both sides, which may or may not have constricted slightly the available width for passage.

We can try 120 feet (maximum) and 90 feet (minimum) for the width of the bridge.  We have to get 1,700,000 soldiers across it in a specific time interval, which Herodotus gives as seven days and seven nights of continuous operation.

I am going to assume half normal walking speed to cater for organisational slackness and muddle, intervals between units and other potential sources of delay and hindrance.  This gives a speed of advance of 1.5 miles per hour, or 2,640 yards per hour.  Herodotus mentions the troops crossed 'under the lash' so they presumably did not dawdle.

I shall further assume that the men moved across with an individual depth and frontage of six feet.  This may be over-generous but at least we know that whatever number passes through is not being over-estimated.

With a 120-foot wide bridge we get 120/6 = 20 men abreast.  The rate of advance is 2,640/2 = 1,320 men per hour per file.  The bridge allows 20 files abreast.  This brings 1,360x20 or 26,400 men over the bridge every hour.

There are 24 hours in the day and Herodotus tells us the crossing was non-stop.  26,400x24 = 633,600 men per day.  In three days 1,900,800 men could have crossed under these circumstances, i.e. the bridge had the capacity to pass double the force given by Herodotus in the time period specified.

Assuming a bridge only 90 feet wide brings 3/4 of that total, i.e. 1,425,600 men, across in this same three-day period.

The baggage crossed by its own separate bridge, so does not need to be reckoned into this calculation.

What this demonstrates is that given the details in Herodotus, Xerxes' army could have been a lot larger than Herodotus mentions.  Specifically, as it took seven days and seven nights to cross, it could have been double the size Herodotus gives.

Xerxes' army thus passes with flying colours the only time-and-motion constriction study for which we have any sort of figures.  Indeed, there is much potential slack in their throughput, which allows for a considerable level of sloth in the process.  Adding in 100,000 mounted troops including a number of chariots adds little to the timing: allowing horses 20 wide with 6' frontage per animal and 9' of depth per animal and crossing at the same speed (e.g. if the men are leading their mounts) brings over 880x20 = 17,600 cavalry per hour so about six hours to clear the lot.  Add another two hours for a 90' wide bridge.  Everyone is still over in about half the stipulated time.

We can even drop the average rate of advance to a sluggish three quarters of a mile per hour and everyone still makes it over within the time limit.

[Dangun]

Xerxes' army thus passes with flying colours the only time-and-motion constriction study for which we have any sort of figures.

While that is interesting, it is not what I meant. I apologise for being unclear.

I was asking whether there were different examples from history, where so many soldiers, passed through such a small space (as your bridge), in such a small amount of time.

A pattern of comparable examples will mitigate incredulity.

[Mark G]

To repeat a previous question.
.what is your basis for this generally accepted 10% + 10% man power rule?

[Patrick Waterson]

To repeat a previous question.
.what is your basis for this generally accepted 10% + 10% man power rule?

The same as those who habitually employ it.

Since this is not explained with every use, it goes something like this.  Traditionally, in most populations, men from 16 to 60 can be expected to perform military service with at least some effect.  Everyone else is too young, too old or too female to be considered (except among Amazons).  Given the usual population distributions by age and gender demographers have come to expect throughout history, this means that 20% of the population is usually male and 16 to 60.  Those best capable of military service are the 18 to 40 year olds, who are about equal in number to the 16-17 year olds plus the 41-60 year olds.

These numbers will not be true of absolutely every society everywhere, but they are good enough for the societies normally studied in a military context.

[Patrick Waterson]

Xerxes' army thus passes with flying colours the only time-and-motion constriction study for which we have any sort of figures.

While that is interesting, it is not what I meant. I apologise for being unclear.

I was asking whether there were different examples from history, where so many soldiers, passed through such a small space (as your bridge), in such a small amount of time.

A pattern of comparable examples will mitigate incredulity.

There were, although the problem is that historians need to have taken the trouble to record them.  We have, for example, no figures for how many of Maxentius' soldiers managed to rout across the Milvian Bridge (AD 312) before it collapsed, or the bridge's dimensions.  If we could find the campaign archives of Thutmose III we might have firm figures for his army size and transit time for the Beth-horon pass; this was also traversed (under opposition) by Cestius' army of occupation in AD 66 but we lack the strength of his army and the time of transit.  What we do get is:

"Now the Jews did not so much press upon them when they were in large open places; but when they were penned up in their descent through narrow passages, then did some of them get before, and hindered them from getting out of them; and others of them thrust the hinder-most down into the lower places; and the whole multitude extended themselves over against the neck of the passage, and covered the Roman army with their darts." - Josephus, Jewish War II.19 [547] (Whiston)

Not sure if that particularly helps.

Usually what we get is something like:
"Learning that the enemy were near, Marius rapidly crossed the Alps, and built a fortified camp along the river Rhone. Into this he brought together an abundance of stores, that he might never be forced by lack of provisions to give battle contrary to his better judgment." - Plutarch, Caius Marius 15.1-2

Not ideal for analysis, but at least a substantial force 'rapidly crossing' a restricted transit point.  As for the opposition, who are given as at least 300,000 fighting men plus women, children etc.
"The Barbarians divided themselves into two bands, and it fell to the lot of the Cimbri to proceed through Noricum in the interior of the country against Catulus, and force a passage there, while the Teutones and Ambrones were to march through Liguria along the sea-coast against Marius." - idem 15.4

"On the part of the Cimbri there was considerable delay and loss of time, but the Teutones and Ambrones set out at once, passed through the intervening country, and made their appearance before Marius. Their numbers were limitless, they were hideous in their aspect, and their speech and cries were unlike those of other peoples. They covered a large part of the plain, and after pitching their camp challenged Marius to battle." - idem 15.5

Again, our parameters are 'the Ligurian sea coast', 'set out at once, passed through the intervening country' and 'limitless numbers'.  This gives effect rather than information.

So while we can say that there are other recorded cases of large armies moving through small or seemingly small spaces (and these are not the only ones), they are not properly quantified.  If this is satisfactory, all well and good.  If not, we shall probably need a time machine.

[Erpingham]

There is a lot of evidence of Achaemenid bureaucracy lying around, whether hides in Egypt or clay tablets in Babylon.  We also have, for example, Diodorus' accounts of the attempts to reconquer Egypt, involving significant numbers (220,000 men and 600 triremes first time round; 330,000 men and 600 triremes the second time)and extensive preparations over more than one year.  This suggests a high level and degree of organisation.

Well, assuming Diodorus has the correct figures, these armies deploy 5-10% of Xerxes army.  The issue isn't that the Achaemenids could organise or that they had big armies.  Your belief in Herodotus' figures demands a level of organisation above all pre-modern armies. 

How about a totally different social structure and level of technology?

This would, if anything, work in favour of a higher mobilisation percentage because nobody is needed to man all the technology (factories, power stations, railways, etc.).

Exactly - to get 10% you need a different society and/or more technology

Our friends in Livescience estimate that

"From the middle of the third to the end of the second centuries B.C., the adult male population was estimated to have risen from about 200,000 to 400,000 individuals."

The best study I found was this paper.  The military is specifically refered to on p11-14.  I think the weak point is he only addresses citizen numbers, so if you want to get a percentage of the population as a whole, as opposed to the militarily qualified population, you need to add those slaves in, which I did based on a general consensus that about 1/3 of the population were unfree.

I suspect our lack of solid figures will take us nowhere with this line of argument.

If you feel that point has been reached, we can call it a day.
[/quote]

Certainly.

[Erpingham]

So while we can say that there are other recorded cases of large armies moving through small or seemingly small spaces (and these are not the only ones), they are not properly quantified.  If this is satisfactory, all well and good.  If not, we shall probably need a time machine.

I think the question is not whether ancient armies could move through passes or on coast roads but whether 4.5 million men could do this.  We lack a precedent.  When armies approaching this size were deployed in later history, they were spread over much larger fronts. 

[Mark G]

Ok, thanks Pat.

So no evidence but you're going to keep repeating it as an established truth, even though you can't provide other people using those numbers either. 
Fine, carry on.
Just wanted to be clear on that.

[Patrick Waterson]

Well, assuming Diodorus has the correct figures, these armies deploy 5-10% of Xerxes army.

And they appear to involve only one mobilisation area, Syria-Phoenicia, rather than the six areas I have identified within the Empire.  Xerxes used all six.  Each area appears to supply 300,000 men when called upon, or some portion thereof (the 373 BC invasion of Egypt used 200,000 while the 343 BC invasion appears to have used the full 300,000).  We may note that in Xenophon's Anabasis Cyrus the Younger breaks with tradition and brings only the best 100,000 from Asia Minor - he is met by 900,000 of the 1,200,000 Artaxerxes pulled together from four of the six areas.

The issue isn't that the Achaemenids could organise or that they had big armies.  Your belief in Herodotus' figures demands a level of organisation above all pre-modern armies. 

Is there a problem with this?

One may note that during the classical period men were very conscious that mankind and civilisation were declining as time went on, a golden age having been succeeeded by a silver age, then a bronze age, then an iron age.  This impression is interesting given that our historians think that mankind and civilisation were progressing during this period.

The sticking-point many people seem to have about Xerxes' army is its uniqueness (well, almost uniqueness).  It was the largest army the Achaemenids ever fielded.  It also suffered the most catastrophic consequences of any Achaemnid campaign.  Is it really so surprising that it was never repeated?

How about a totally different social structure and level of technology?

This would, if anything, work in favour of a higher mobilisation percentage because nobody is needed to man all the technology (factories, power stations, railways, etc.).

Exactly - to get 10% you need a different society and/or more technology

Less technology.  The more technology you have, the more people are tied down keeping it going and are not free for military service.  Low technology societies can mobilise a greater proportion of their manpower.  As you rightly observed, mobilisation is essentially a matter of organisation.

The best study I found was this paper.  The military is specifically refered to on p11-14.  I think the weak point is he only addresses citizen numbers, so if you want to get a percentage of the population as a whole, as opposed to the militarily qualified population, you need to add those slaves in, which I did based on a general consensus that about 1/3 of the population were unfree.

Actually addressing just citizen numbers is much better than trying to count in slaves. Slaves will tend to distort age groups and are not usually available for military service (they are in some cultures but not usually the ones we tend to be interested in).  Besides, slaves are replaceable after a successful camapign whereas military manpower is more of a constant (occasional major disasters aside).

I observe that the assumed free population for Italy under Republican Rome (3-3.5 million) ties in very nicely with Polybius' 700,000 men of military age in Italy during the same period.  The writer does issue caveats about consistency not necessarily meaning accuracy, but that is just covering himself.  Where one finds consistency accuracy (insofar as one can obtain such at this remove in time) is rarely far away.

I think the question is not whether ancient armies could move through passes or on coast roads but whether 4.5 million men could do this.  We lack a precedent.  When armies approaching this size were deployed in later history, they were spread over much larger fronts. 

The 'later history' is about 2,500 years later and the greater frontages a function of ranged breech-loading firepower more than anything else.  By 1914, long gone were the days when depth meant stability on the battlefield - as of the gunpowder era, great depth essentially meant extra casualties.  (One could point out that deeper formations, e.g. the Napoleonic column, did add stability, and this is true; and that they increased casualties, which is also true.  The battlefield attack column died a natural death in AD 1866 and has not been seen since.)  The change in combat technique over the intervening period means we are not comparing like with like.

[Flaminpig0]

Less technology.  The more technology you have, the more people are tied down keeping it going and are not free for military service

The conventional view is that technology generally makes individuals more productive  and thus modern societies have a large number of individuals not directly employed in producing food stuffs etc.

[Mark G]

18th century columns were not deep as you convey them.

They were a series of parallel lines with space between for linear deployment.

[Dangun]

So while we can say that there are other recorded cases of large armies moving through small or seemingly small spaces (and these are not the only ones), they are not properly quantified.  If this is satisfactory, all well and good.  If not, we shall probably need a time machine.

Agreed. The sources are not entirely cooperative.

There were, although the problem is that historians need to have taken the trouble to record them.  We have, for example, no figures for how many of Maxentius' soldiers managed to rout across the Milvian Bridge (AD 312) before it collapsed, or the bridge's dimensions.  If we could find the campaign archives of Thutmose III we might have firm figures for his army size and transit time for the Beth-horon pass; this was also traversed (under opposition) by Cestius' army of occupation in AD 66 but we lack the strength of his army and the time of transit.

These are interesting precedents, and perhaps equivalent in terms of density. I will certainly google Beth-horon now.
But they don't have the scale. At least 1, maybe 2 orders of magnitude smaller.

Herodutus' number pushes me to the wrong end of the credulity continuum, because it is such an unprecedented combination of density and scale.