The effect of religion on the army

[Jim Webster]

The fact that there are laws banning things mean people are doing it.

I would suggest that the ban on men fighting was every bit as effective as the Papal ban on the use of the crossbow.
Or perhaps the Roman Catholic church's restrictions on contraception

With the others, remember that fellow bishops were social equals and often friends. Many where from the same background.


Jim

[Mark G]

There are people eating humans in Britain?  Having relations with corpses?

Just because its banned doesn't mean people are doing it,
It just means that someone thinks they might do it if they thought it was allowed.

[aligern]

Late Antique and Early Medieval laws are generallly the product of the legal process. Cases would be brought and judgements given. Where a judgement was novel or involved a particular twist of logic it might make it into an issued update of the law code. Where a situation occurred where the law was in doubt then that might getupdated or clarified and that could give the state an oppirtunity to push things further. So there are laws about the relationship of the buccelarius with his lord because this was a new relationship and someone had likely found an old law did not give them what they wanted and appealed and got case law which then became generally promoted.
There is a law in the Lombard laws about someone who shoots  an arrow into a compound and kills or wounds someone else. Presumably this is based on an actual case and revolved around the difficulty of equating a death so caused with an accident. What happens if twenty people shoot at once?
A law might mean that a lot of an activity was going on, like the buccelarius relationship or extremely rare like shooting in a compound, or theoretical and the result of gold plating by some clerk.
An interesting case is Wamba's army law in The Spanish Visigothic post  Roman kingdom. Is Wamba  legislating for a society with an army comprised of slaves or is this a specific response to a recent rebellion, where landowners have sat on the sidelines when a rebel made a bid fir the throne and the king, rebellion defeated, wants to impose very clear obligations on a group of landowners that they must turn up and the armed slaves referred to are not the main army which is a tax based force in garrisons. The law Wamba passed looks very like a loophole being closed, but is it a loophole which had permitted landowners to stand aside from supporting the king or is it about setting out how the army would recruited now there are not enough free men to staff it?
Roy

[Erpingham]

Making a sweeping generalisation (which seems to be the way of this thread ) , the Western Christian church in the Middle Ages lost absolute pacifism pretty early as it began to expand into a major religion.  It instead started to concentrate more on regulating war, deciding on when it was legitimate to hold a war (against whom, on what days), the role of the military caste in society and the obligations that brought to protect the weak and the clerical establishment, a bit of arms control and so on.  One might seek to judge the effectiveness of some of this, and marvel at the Church's bottomless capacity for hypocricy in delivering it, but it did have an effect on how wars were thought about and, indeed, fought.

[Jim Webster]

There are people eating humans in Britain?  Having relations with corpses?

Just because its banned doesn't mean people are doing it,
It just means that someone thinks they might do it if they thought it was allowed.

It's a standard Historians comment when discussing, for example, the repetition of laws under Roman Emperors. If seven or eight consecutive emperors feel the need to instruct Roman soldiers not to rob or mistreat unarmed civilians, then soldiers robbing and mistreating unarmed civilians must be a problem.
So if various theologians and similar are constantly having to remind people that you're not supposed to fight in the army, then Christians must be fighting in the army.

Where laws are generally obeyed (as in your example of cannibalism or necrophilia) they are rarely if ever repeated. In fact cannibalism is so little a problem in the UK that it isn't in itself illegal, (it might be because you could be charged with incorrect disposal of a body or under food hygiene regulations) but killing someone to eat them is

On the other hand, road safety is an issue and is repeatedly legislated over because many people are largely ignoring the rules.

Jim

[Patrick Waterson]

So if various theologians and similar are constantly having to remind people that you're not supposed to fight in the army, then Christians must be fighting in the army.

A valid comment, in my view.  However - and this is an important however - on the topic of the effect that such theologians are having on the Empire's ability to defend itself, a constant succession of injunctions from presumably respected religious leaders to a presumably significant part of one's soldiery that they are not supposed to fight would hardly be helping the combat capability and morale of the army.  Being classed in the same bracket as thieves is also hardly conducive to soldierly morale.

Couple this with Basil's apparently respected and enforced admonition that if you kill an enemy of the Empire you get three years' suspension from communion and the surprise is that sufficient soldiers were being found who were willing to do their duty.

Or were there?

Following the death of Basil (of Caesarea and the eponymous canons) c.AD 379, the Roman world ended up with Theodosius as emperor via Gratian.  Whilst up to Gratian Roman soldiery seem to have still been substantially Mithraic, Theodosius appears to have taken steps to eliminate Mithraism and make the army wholly Christian.  However, when Arbogast put Eugenius in charge of the west, Theodosius seems to have needed to call upon his Gothic 'allies' in order to acquire sufficient force to deal with Eugenius - and even then it was a close-run thing.  In the absence of hard evidence (or awareness of hard evidence) one is reduced to speculation: was Theodosius running short of Empire-born Roman soldiers?  Was his elimination of Mithraism the factor that tipped recruitment into debit, forcing increasing reliance on barbarian allies and indeed recruits to make up numbers and fighting power?

Making a sweeping generalisation (which seems to be the way of this thread ) , the Western Christian church in the Middle Ages lost absolute pacifism pretty early as it began to expand into a major religion.  It instead started to concentrate more on regulating war, deciding on when it was legitimate to hold a war (against whom, on what days), the role of the military caste in society and the obligations that brought to protect the weak and the clerical establishment, a bit of arms control and so on ...

The western church actually evolved outside the Roman Empire.  It began to diverge from the eastern c.AD 595 with the adoption of the Latin liturgy (the Orthodox church based in Constantinople was by then using Greek) and following some mutual spats about authority the split became real when the Latin church, the antecedent of today's Roman Catholics, adopted the filio que.  A word of explanation may be in order.

Greek Orthodox liturgy held that the Holy Spirit proceeded from the Father (only).  The Latin church developed the opinion that as the Father and Son were equal and the same being, the Spirit must therefore also proceed from the Son.  In Latin, 'and from the Son' is 'filio que', hence the name of this particular controversy.

It was this church, the Latin or Catholic church, which sought to regulate rather than make a blanket condemnation of warfare.  One reason was because in the west the Papacy was angling for temporal influence, and even rulership, over the western European nations, so it saw itself in the role of semi-pragmatic legislator (the nations involved had a different idea, hence when the western church forbade the use of crossbows against Christians everyone pretty much ignored it).  The eastern or Orthodox church, although in theory very much subordinate to the state, continued to drag its feet and condemn warfare as murder (although in a later century it would tacitly underwrite the practice, if not the theory, of holy war against the Crusaders of 1204 who attacked Constantinople).

[Justin Swanton]

When a state gains a single 'unifying' religion (or else) it creates a much deeper divide and matter of grievance against those who follow false gods, no gods, the same gods but in a significantly different way.

To illustrate...

[Jim Webster]

https://www2.bc.edu/marian-simion/th406/readings/0314simion.pdf  has an interesting take on the Orthodox attitude to war.
Notable is the debate as to whether Gregory's canon was ever enforced.

One of the big differences between east and west was actually the role of the Emperor. The west didn't have one and the Pope tried to step into the gap (hence a partial explanation of the conflict between popes and the German Emperors.)

So in Eastern thinking, the Emperor was placed by God in charge of the state was was above the church. The church merely advised, they didn't order the Emperor

Jim

[Justin Swanton]

It is interesting to note that these 'active bishops' (Synesius of Cyrene and Sidonius Apollinaris) tend to be out-and-out Hellenists without a discernible shred of Christian belief.  Also that they are stepping into the gulf left by the division of responsibility into 'civil' and 'military' that has scrambled the efforts of many a western civilisation since.

Sidonius is remarkable for the total absence of Christian sentiment in his writings until he became bishop. He took the loss of Clermont and his Roman citizenship very badly - which a true dyed-in-the-wool Christian would have taken with far more philosophical (or religious) resignation. Compare him to Augustine, especially Civitas Dei. Sidonius was not a typical example of a bishop - he wasn't sainted - so one can hardly use him as an example of the mentality of the Catholic hierarchy at that time.

There is certainly evidence that Christians were in the Roman army in Diocletian's time, although how many of these were serving soldiers who had converted as opposed to Christians from birth who had enlisted is not clear.

The point is they were in the army and sufficiently clear in their principles to accept martyrdom for their faith, i.e. they were committed Christians who saw no contradition between being a Christian and being a soldier. Christianity is not pacifist nor does it have to be.

And tombstone inscriptions tend to skirt around this sort of thing.  Once we are well into the Byzantine Empire, yes, the soldiery are Christian, but that brings its own set of problems, of which an inability to fight well at Easter because God is (temporarily) dead is perhaps the least of the concerns.

Easter is actually about a God made man who overcomes death and pays for the sins of men in the bargain. The Church may have sought to have its soldier members not fight during Holy Week as this was a time to take a distance from worldly occupations and focus on important aspects of their faith, but if fighting was necessary then of course they had the Church's blessing to get on with it.

Militant Islam proved a tough adversary for pretty much anyone, Christian or not. The Byzantines did a lot better than the Sassanians, who were completely overrun in the course of a few years.

The Byzantines were actually pretty much on the ropes by the late 7th century AD, with Constantinople twice under siege; conventional wisdom has it that they owed their deliverance to the timely invention and application of Greek Fire.  Thereafter, sad to say, the Empire probably owed its continued survival as much to Muslim internal division as to the capabilities of its armies and generals and its somewhat overdeveloped sense of diplomacy.

The Empire got off the ropes in the 10th century, beginning a campaign of reconquest that regained the Balkans and eventually got them into Antioch. The fact that Byzantium survived Islam's first phase as a unified empire whilst everyone else went down like ninepins sufficiently attests to its military prowess on land and sea.

If you compare the Byzantine Empire to any other state in history it comes off  remarkably well, surviving ultimate conquest for a thousand years. No pagan empire managed anything like it.

One could make the same comment about the Holy Roman Empire.  Yet both seem to have a yawning gap in achievement and a grovelling lack of dignity compared to, say, the shorter but brighter stars of Egypt and Macedon: longevity seems to have been purchased at the price of senescence.

This transposes onto the subject of whether a civilisation is 'worthwhile' or not, independent of its military capabilities. I would say that from the point of view of culture, ancient Egypt's veins were a good deal harder that Byzantium's. That stereotyped two-dimensional art that never changed with the exception of one pharaoh's reign.

Macedonia spread Greek culture into the east, but that culture - especially the intellectual culture - did not develop in Macedonia itself. About the only thing you can strictly credit the Macedonian and Successor empires for is a superior military system.

All the major religions IMHO cater for the army to some extent, i.e. they incorporate in their belief system a reason for soldiers to fight.

Not too sure this applies to Buddhism; if anything, there seems to have been a tradition that fighting and religion are kept strictly apart.  As for the Byzantine Empire, Gibbon notes (chapter 53) that Nicephorus Phocas, one of the more successful emperors, sought to "bestow the honours of martyrdom on the Christians who lost their lives in a holy war against the infidels."  He cites Zonaras and Cedrenus as mentioning that "the patriarch, the bishops and the principal senators ... strenuously urged the canons of St Basil, that all who were polluted by the bloody trade of soldier should be separated, during three years, from the communion of the faithful." (See his footnote 83 to the 53rd chapter.)  Something of a let-down for the soldiery of the Empire, methinks, returning home as ex officio excommunicants.

Bearing in mind this is a single case of an emperor going too far - soldiers who die in combat are not martyrs - and the hierarchy reacting against him, possibly going too far in the other direction. It doesn't really represent the settled attitude of Byzantine society towards its soldiery, and attitude that would have affected the soldiers themselves and their subsequent performance.

Christianity is no exception to this, as the efficiency and professionalism of the Byzantine army demonstrates.

Might I suggest this may be confusing the influence of religion with that of military doctrine and practice?  The Taktikon and Strategikon were not exactly Christian documents.

No, but the soldiers were, and their state of mind would determine how effectively they lived and fought by those manuals.

Gibbon (chapter 53) himself concludes:

"... the Greek superstition relaxed the mind by prayer, and emaciated the body by fasting; and the multitude of convents and festivals diverted many hands and many days from the temporal service of mankind."

Apart from the provision of the occasional sacred standard, this seems to have been the sum of its contribution to the Imperial war effort.

That's Gibbon's point of view. Can he substantiate it?

If an empire loses land or is completely overrrun it is due, again IMHO, to unforeseen circumstances: a new military system in the case of the Achaemenid Persians, a division at the highest levels of government for the Western Romans, or just a bad day for the army like Manzikert or Myriocephalum for the Byzantines.

Or a stronger opponent or poor leadership - or exceptional leadership on the other side.  True, most empires do not foresee their own collapse (the Roman may have been an exception, thinking of the Sibylline Books), but let us not underrate the value of a straight fight for determining who does what unto whom.  The Byzantines became famous for 1) their avoidance of straight fights and 2) their use of gold and other aspects of diplomacy to try and keep opponents busy and/or quiescent.  Byzantine conquests or reconquests tended to be short-lived affairs, not least because of domestic problems, many of which were religious in nature (iconoclasm, monothelitism or just application of the canons of St Basil) and some of which were admittedly just the usual selection of bad characters whose ambition also exceeded their ability.

The reconquests of Basil in the Balkans were pretty permanent, and the point about Byzantine avoidance of straight battles is that it is sound military doctrine. However the army was always prepared for a straight battle if one was necessary - and it fought quite a few!

[Patrick Waterson]

Sidonius was not a typical example of a bishop - he wasn't sainted - so one can hardly use him as an example of the mentality of the Catholic hierarchy at that time.

Indeed, like Synesius he was au fond a Hellenist.  However, like Synesius, he was used as an example of a 'military' bishop apparently exemplifying a robust Christian approach to warfare, and yours truly was simply pointing out the correlations between such bishops and a Hellenistic weltanschaung.

There is certainly evidence that Christians were in the Roman army in Diocletian's time, although how many of these were serving soldiers who had converted as opposed to Christians from birth who had enlisted is not clear.

The point is they were in the army and sufficiently clear in their principles to accept martyrdom for their faith, i.e. they were committed Christians who saw no contradition between being a Christian and being a soldier. Christianity is not pacifist nor does it have to be.

Orthodox Christianity under the Empire was selectively pacifist.  On the one hand we have soldiers being discouraged from fighting and excommunicated if they do so successfully: on the other we have the uninhibited spirit of unbridled fanaticism whenever a question of doctrine arises, with no mercy shown to the loser.

Easter is actually about a God made man who overcomes death and pays for the sins of men in the bargain. The Church may have sought to have its soldier members not fight during Holy Week as this was a time to take a distance from worldly occupations and focus on important aspects of their faith, but if fighting was necessary then of course they had the Church's blessing to get on with it.

This does not seem to be how the Byzantine soldiery at Callinicum saw the matter.  As far as they could see, God (in the form of Jesus) was dead and buried on Friday and back up on Sunday*, albeit not such an early riser as the Persians, hence the defeat.

*(or late on Monday if he actually spent three days in the tomb)

The Empire got off the ropes in the 10th century, beginning a campaign of reconquest that regained the Balkans and eventually got them into Antioch. The fact that Byzantium survived Islam's first phase as a unified empire whilst everyone else went down like ninepins sufficiently attests to its military prowess on land and sea.

Yes and no - and not everyone else went down like ninepins.  The Visigoths did (having a civil war at the time did not help); the Franks did not.  Subsequent history in the Iberian peninsula is termed the Reconquista for a good reason - and unlike the Byzantine gains, the Portuguese Leonese, Aragonese and Castilian gains were eventually parlayed into complete conquest of the Iberian territories.

If you compare the Byzantine Empire to any other state in history it comes off  remarkably well, surviving ultimate conquest for a thousand years. No pagan empire managed anything like it.

One could make the same comment about the Holy Roman Empire.  Yet both seem to have a yawning gap in achievement and a grovelling lack of dignity compared to, say, the shorter but brighter stars of Egypt and Macedon: longevity seems to have been purchased at the price of senescence.

This transposes onto the subject of whether a civilisation is 'worthwhile' or not, independent of its military capabilities. I would say that from the point of view of culture, ancient Egypt's veins were a good deal harder that Byzantium's. That stereotyped two-dimensional art that never changed with the exception of one pharaoh's reign.

Were I of a mean disposition, I might put: "Ah, like icons."

Macedonia spread Greek culture into the east, but that culture - especially the intellectual culture - did not develop in Macedonia itself. About the only thing you can strictly credit the Macedonian and Successor empires for is a superior military system.

And the spread of a modified Hellenic culture that became known as Hellenistic - and which, when interleaved with Roman law and attitudes, served as the basis of what we know as western civilisation.

... Gibbon notes (chapter 53) that Nicephorus Phocas, one of the more successful emperors, sought to "bestow the honours of martyrdom on the Christians who lost their lives in a holy war against the infidels."  He cites Zonaras and Cedrenus as mentioning that "the patriarch, the bishops and the principal senators ... strenuously urged the canons of St Basil, that all who were polluted by the bloody trade of soldier should be separated, during three years, from the communion of the faithful." (See his footnote 83 to the 53rd chapter.)  Something of a let-down for the soldiery of the Empire, methinks, returning home as ex officio excommunicants.

Bearing in mind this is a single case of an emperor going too far - soldiers who die in combat are not martyrs - and the hierarchy reacting against him, possibly going too far in the other direction. It doesn't really represent the settled attitude of Byzantine society towards its soldiery, and attitude that would have affected the soldiers themselves and their subsequent performance.

The problem was that the Empire's opponents who died in combat were martyrs, and Nikephorus, unlike his closed-minded clerics, saw that unless the playing-field was levelled then the Muslims would always have a morale advantage, whereas the Empire would not always have capable soldier-emperors.

Gibbon (chapter 53) himself concludes:

"... the Greek superstition relaxed the mind by prayer, and emaciated the body by fasting; and the multitude of convents and festivals diverted many hands and many days from the temporal service of mankind."

That's Gibbon's point of view. Can he substantiate it?

Yes, in chapters 47, 49 and 53.

The reconquests of Basil in the Balkans were pretty permanent, ...

Granted they lasted for about 170 years, although it only took Isaac Angelus a few months to lose them permanently.

... and the point about Byzantine avoidance of straight battles is that it is sound military doctrine. However the army was always prepared for a straight battle if one was necessary - and it fought quite a few!

Indeed, although to Norman-dominated Europe and even the Muslim-dominated Near East this behaviour, which if anything compares favourably with the standards and methods of today, smacked of deviousness and cowardice together and seems to have encouraged attack as often as it parried or avoided it.  The real problem was not so much keeping the frontiers defended (the Byzantines were usually pretty good at that when it came to the crunch) but what went on within those frontiers.  This as much as anything else is what made Byzantine recoveries rather hesitant and short-lived affairs.

[Jim Webster]

I confess to having always enjoyed the irony that now Christianity is blamed, often simultaneously, for having been pacifist and led to the fall of the Roman Empire, and also to have led to the deaths of countless millions through crusades and persecutions etc

Jim

[Justin Swanton]

Indeed, like Synesius he was au fond a Hellenist.  However, like Synesius, he was used as an example of a 'military' bishop apparently exemplifying a robust Christian approach to warfare, and yours truly was simply pointing out the correlations between such bishops and a Hellenistic weltanschaung.

Or one could point out that the default stance of bishops who had been left with the administrative responsibility for their towns was not pacifist when it came to dealing with barbarian attacks. Sidonius acted as a bishop with no particular reference to hellenism.

Orthodox Christianity under the Empire was selectively pacifist.  On the one hand we have soldiers being discouraged from fighting and excommunicated if they do so successfully: on the other we have the uninhibited spirit of unbridled fanaticism whenever a question of doctrine arises, with no mercy shown to the loser.

Unlike the West, the Church in the East became a department of state, which means its doctrines and moral praxis became intimately bound up with the fabric of Byzantine society. If the Eastern Church really had opposed soldiery, there would quite simply have been no Byzantine army. One needs to examine the extent to which this excommunication actually had meaning or effect.

This does not seem to be how the Byzantine soldiery at Callinicum saw the matter.  As far as they could see, God (in the form of Jesus) was dead and buried on Friday and back up on Sunday*, albeit not such an early riser as the Persians, hence the defeat.

I haven't looked at Callinicum in detail, but the point remains that the Byzantine army was in general ready to fight with the Emperor's and hence the Church's blessing.

Yes and no - and not everyone else went down like ninepins.  The Visigoths did (having a civil war at the time did not help); the Franks did not.  Subsequent history in the Iberian peninsula is termed the Reconquista for a good reason - and unlike the Byzantine gains, the Portuguese Leonese, Aragonese and Castilian gains were eventually parlayed into complete conquest of the Iberian territories.

The Umayyad Caliphate was beginning to unravel at the time of the invasion of Gaul, and one can argue that Charles Martel had a good deal of luck (or Providence?) on his side, catching the Moors by surprise and obliging them to fight a battle with the terrain in his favour. He could, in different circumstances, quite easily have lost the battle.

The difference between Gaul and the Byzantine empire is that the Moors did not repeatedly attempt to conquer the Frankish kingdom, whereas they did launch repeated attacks against Byzantium which beat them all off.

Were I of a mean disposition, I might put: "Ah, like icons."

OK, that makes two old men with hardened arteries.

BTW I don't particularly think Byzantine civilisation compares very well with the West once the West had got back on its feet following the chaos of the 9th and 10 centuries.

The problem was that the Empire's opponents who died in combat were martyrs, and Nikephorus, unlike his closed-minded clerics, saw that unless the playing-field was levelled then the Muslims would always have a morale advantage, whereas the Empire would not always have capable soldier-emperors.

Islam saw the jihad - making war against and conquering the lands of non-believers - as a sacred duty, which Christianity has never done. It's this outlook that makes Islam the only religion today to produce religiously-motivated suicide bombers.

Yes, in chapters 47, 49 and 53.

I'll look them up. 

Indeed, although to Norman-dominated Europe and even the Muslim-dominated Near East this behaviour, which if anything compares favourably with the standards and methods of today, smacked of deviousness and cowardice together and seems to have encouraged attack as often as it parried or avoided it.  The real problem was not so much keeping the frontiers defended (the Byzantines were usually pretty good at that when it came to the crunch) but what went on within those frontiers.  This as much as anything else is what made Byzantine recoveries rather hesitant and short-lived affairs.

The bottom line though is that the army did its fundamental job: defend the empire for centuries.

[aligern]

The weakness of the Byzantines is that they were subjected to unrestricted immigration and lacked a policy that acculturated the newcomers.  In the West they might have reconquered the territories, but the Balkans had more the aspect of a multi state federation than of a homogenous state. Hence, when the Byzantines lost a couple of battles the territory reverted to being Serbiaor Bulgaria. Similarly in Anatolia, once the Turks had flooded in and reduced the territory to Nomad pastureland dotted with agreek citiesthe basis of the army tied to Byzantine land had gone.nByzantium had another life as a commercial empure and this carried on and was able to hire mercenaries, but as a territorial state the Greeks were doomed. Their religion played a part in this in two ways. Firstly they sought to acculturate the Balkan immigrants , Slavs and steppe dwellers, by converting them, but this only went so far as the translation of Christianity into national Orthodox churches did not turn these territories back into provinces, but simply co religionist states. Secondly Greek Orthodox Christianity always had a strong pacifist thread and it did not provide an impetus to conquest. Hence the Empire mainly lost territory and defended rather than seeking to acquire territory. At best it attempted to get back minor list areas such as Sicily and Southern Italy or Crete and Cyprus. Given the effectiveness of the Basilian army the amount of territory reconquered from the Moslems was pathetic. At a time when. they were strong and their enemies divided the Byzantines could not reconquer Syria and Egypt. To an extent this is because they had not kept the Balkans as a homogenous part of the empure, Greek speaking, colonised by imperial peasants, raising imperial armies. To an extent it also due to their defensive minded ness and the lack if a theology of aggression.
Roy

[Patrick Waterson]

Good observations, Roy.  It is particularly noticeable in the case of the Bulgars that the Byzantines pretty much converted them and left it at that, i.e. put no real effort into assimilating and civilising them.  One gets the impression that Byzantine victories were thrown away because of this tendency to think that converting barbarians and/or cleansing altars used by the Azymites was all one really needed to do to re-establish the Empire.

When the Byzantine army did fight, it was not always successful.  If one looks at the Wikipedia list of Byzantine battles, it is depressing (especially to a Byzantine army admirer like myself) how many they managed to lose!

Or one could point out that the default stance of bishops who had been left with the administrative responsibility for their towns was not pacifist when it came to dealing with barbarian attacks.

A complete list of such bishops might be helpful to allow us to draw conclusions.

If the Eastern Church really had opposed soldiery, there would quite simply have been no Byzantine army. One needs to examine the extent to which this excommunication actually had meaning or effect.

Hmmm ... as the emperor was supreme, it was he and not the church who determined whether there would be an army (Constantine Ducas, for example, seemed to consider one largely unnecessary).  The excommunication would however seem to have had meaning and effect if Nikephorus Phocas wanted to change the rules.

The Umayyad Caliphate was beginning to unravel at the time of the invasion of Gaul, and one can argue that Charles Martel had a good deal of luck (or Providence?) on his side, catching the Moors by surprise and obliging them to fight a battle with the terrain in his favour. He could, in different circumstances, quite easily have lost the battle.

Surprising Moors was apparently more a matter of routine than of luck.  Duke Odo (Eudes) of Aquitaine did the same with more effect, in the Battle of Toulouse in AD 721.

Tours was by no means a once-for-all success.  Charles Martel continued to pull off successes at Narbonne and the River Berre in AD 737, and Pepin the Short made the expulsion of the Muslims permanent by capturing Narbonne itself in AD 759 after a long siege.  Ummayad rule had remained more or less intact until AD 750, which may be why Carloman and Pepin the Short had not pushed further earlier, but the essence of the matter is that the Franks were warlike where the Byzantines were not, and their version of Christianity seemed to be more flexible or at least reticent about such things as smiting opponents, whether unbelievers or no.

The real problem was not so much keeping the frontiers defended (the Byzantines were usually pretty good at that when it came to the crunch) but what went on within those frontiers.  This as much as anything else is what made Byzantine recoveries rather hesitant and short-lived affairs.

The bottom line though is that the army did its fundamental job: defend the empire for centuries.

Up to a point.  What is however very noticeable is that it did not regain lost imperial territories with any great vigour or consistency, and ended up being largely a collection of foreign mercenaries (Varangians, Latinikon, Vardariots and Skythikon) rather than native troops, and this at a time when Orthodox insistence on the need to stand against Azymite heretics was at its most clamorous.

I confess to having always enjoyed the irony that now Christianity is blamed, often simultaneously, for having been pacifist and led to the fall of the Roman Empire, and also to have led to the deaths of countless millions through crusades and persecutions etc

Would that be a paradox rather than an irony?  In any event, 'Christianity' in its multiform variations managed both (although in crusades it takes two to tango, and the basic purpose of crusades was to liberate conquered Christian lands) and even during the Spanish conquest of the New World one had the 'nice priests' who wanted to turn the natives into a happy thriving Christian community and the 'nasty priests' who thought that as they had been born in sin and worshipped false gods, conquest, robbery and burning at the stake was too good for them.

[Erpingham]

What is however very noticeable is that it did not regain lost imperial territories with any great vigour or consistency, and ended up being largely a collection of foreign mercenaries (Varangians, Latinikon, Vardariots and Skythikon) rather than native troops,

It is, of course, an interesting question both why this was and how important it was.  Did religion make it hard to recruit native troops, or a loss of tradition recruiting grounds?  Also, why is a mercenary army such a bad idea?  Though the latter might be another thread entirely.