Copyright by S. van Dorst 2000
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Under Diocletian the frontier armies bore the brunt of the defence of the empire. The role of the field armies decreased somewhat as political stability meant that usurpations were a lesser threat that they had been before. Each of the tetrarchs had a small sacer comitatus at his disposal. The nucleus of these imperial field armies was formed by guard units and a select number of permanently attached detachments from the provincial armies. For large campaigns these formations were temporarily joined by vexillationes from the frontier forces.
The tetrarchic field armies were made up of a number of different formations. Detachments from the praetorian guards, both infantry and mounted troops like the equites promoti, were permanently attached to the retinue of the emperors. These units were by this date also known as cohortes palatinae. The old equites singulares Augusti still existed as the imperial horse guard, although these guardsmen had traded in their name for equites dominorum nostrorum. New guard units had been created in addition to the old. A mounted schola scutariorum was probably already part of the imperial guard. The unit of protectores consisted of promising men being groomed for higher commands. Elite legionary detachments like the Ioviani and Herculiani drawn from the legio I Iovia Scythica and legio II Herculia and the lancearii recruited among the legionary light infantry were permanently attached to the comitatus. Vexillationes of picked cavalrymen from the frontier units and elite auxilia were also included.
The reign of Diocletian and his fellow emperors saw a massive increase in the number of legions. There were 39 legiones in existence in 286, but this number was almost doubled over the next thirty years. This did not however mean that the total strength of the army was increased on the same scale. Although the structure and establishment strength of these new formations were similar to that of earlier units, some of the tetrarchic legions were formed by combining existing units of the auxilia. These formations were distributed in pairs among the new, smaller provinces. Some new auxiliary units were also created, but the overall strength of the auxilia probably dropped as a result of the formation of legions from auxiliary cohorts.
Recruitment for the enlarged armies proved to be a problem. Not only were old conscription regulations applied with more severity than before, but several new measures were introduced to fill the ranks. Sons of serving soldiers and veterans were now by law required to enlist in the army. The protostasia, a recruitment tax on landownership, was a novel measure. Landowners were obliged to furnish army recruits in proportion to the size and yield of their properties. Those owning only small tracts of land were grouped together and taxed collectively. Not all parts of the empire were subject to levies of men. In the provinces whose population was considered to lack the required martial spirit, the recruiting tax was converted into payments of money known as the aurum tironicum or recruit gold. This money was used to provide bounties to attract volunteers. Men were also recruited from outside the empire, either voluntarily or by the incorporation of barbarian POW's in the army.
The late Roman army contained several different field armies. Some of these, the socalled praesental armies, were under the direct control of the emperors and were the successors to the third century sacer comitatus. Other formations were based in the provinces and served as regional reaction forces. The field army units were composed of both palatini and comitatenses. There were few, if any, differences between these classes of troops, though the former carried more prestige. Cavalry units consisted of vexillationes palatinae and vexillationes comitatenses that provided a mix of heavy, medium and light cavalry. The legiones palatinae, legiones comitatenses and the auxilia palatina consisted mostly of heavy infantry, although some units were also employed as light infantry and archers. The legiones pseudocomitatenses attached to some field armies were detached formations from the frontier armies. A new development was the formation of separate legiones of ballistarii. These formations consisted of artillerymen operating light torsion guns and crossbows.
Unit organisations and establishment strengths for the late Roman army are difficult to reconstruct. Legionary detachments had evolved into seperate units and were now termed legio rather than vexillatio. This meant that a legio could compromise any number between 500 and 5000 men. However 1000 to 1200 soldiers appears to have been a common establishment strength for many of the smaller legions. The internal organisation of these new legions is hard to establish. Although the ancient sources mention centuriae, manipuli and cohortes, the references appear formalistic and may not reflect actual conditions. The auxilia palatina consisted partly of newly raised units, but others had evolved from existing auxiliary cohortes. Their strength and organisation were probably similar to those of milliary cohorts. Cavalry vexillationes are likely to have been 500 strong with internal unit organisation similar to that of the earlier alae. A major break with the past army organisation was the removal of mounted troops previously attached to infantry formations. Units in the late Roman army consisted of either horsemen or foot soldiers, not a mix of both.
Command of the field armies was normally in the hands of senior officers known as magistri, though minor armies could be commanded by a comes. There were some minor variations in the titles of the field army commanders but there appears to have been little difference between the rank and function of a magister equitum, magister peditum or magister militum. Command of units of any kind was by now generally in the hands of a tribunus. These tribunes were professional military officers who had often served as a protector at the imperial court. The tribuni vacantes were officers that were not directly attached to army formations and served in similar capacities as the earlier centuriones supernumerarii. The designation praepositus merely indicated the function of commander rather than an actual military rank. Centuriones were by this date more commonly referred to as ordinarii and centenarii. Officers with identical titles served in both cavalry and infantry units. Optiones recieved the new title of biarchus. Many other new designations for officers and NCO's appear in the sources, but are often difficult to interpret.
Unit titles in the later Roman army were of a slightly different style than those of their early imperial counterparts. Although a lot of units retained names derived from unit numbers, like the Quarti Dalmatae, or their armament, as the Sagittarii Dominici did, there were a few peculiar late Roman practices. Many formations carried the designations of seniores, the 'old ones' or 'veterans', and iuniores, the 'young ones' or 'recruits'. These titles were probably connected to a splitup of the armies among the sons of Constantine that resulted in small cadre forces being detached from existing units to form the backbone of newly recruited formations of the same name. As both types of unit received replacements in an identical fashion iuniores and seniores alike were soon composed of a similar mix of recruits and experienced men. Some late Roman army units also carried barbarian tribal names, but like the titles of earlier auxiliary units these were usually not representive of the ethnic origin of its soldiers, the majority being of Roman rather than foreign extraction.
The frontier forces were entitled limitanei or riparii. These consisted of infantry legiones, cohortes and numeri and cavalry vexillationes, alae and cunei. Frontier legiones were generally but not invariably larger formations than those found in the field armies with a strength and organisation resembling that of the earlier legions. Many units of the limitanei, both legionary and auxiliary, were divided over a number of small fortified bases. Often labelled a peasant militia with low fighting value in modern studies, these troops were in fact professional military units not significantly worse in calibre from those in the field armies. The palatini and comitatenses were regularly supplemented by forces drawn from the frontier armies.
Contrary to popular opinion late Roman troops were as heavily protected by armour as their early imperial predecessors. Although according to the available evidence the famous "lorica segmentata" was no longer in use after the late third century, literary and depictional sources indicate a continued general use of scale, mail and lamellar body armour by both mounted troops and foot soldiers. A padded leather and linen protective vest known as a thoracomachus was worn beneath metallic armour. Additional protection was provided by splinted greaves and armguards, notably in the ranks of the heavy cavalry. Helmet bowls were by this date usually constructed of several segments. The distinction made in some modern works between cavalry and infantry types does not appear to reflect ancient practice. Shields for all troop types were generally of oval or round shape. The unit shield patterns for many field army formations have been preserved in the Notitia Dignitatum, apparently with a remarkable degree of reliability.
Late Roman soldiers carried a variety of missile weapons. The introduction of new names for shafted weapons tends to disguise the fact that there was little essential difference between early and later imperial military practice. Heavy infantry continued to use javelins with long iron shanks similar to the earlier pilum. These could have both pyramidical points for better armour penetration or viciously barbed heads for use against unarmoured targets. Lighter javelins of different types remained the normal equipment of the cavalry, the light infantry and the rear ranks of infantry formations. There may however have been a greater emphasis on longer range fire power. A genuinely new addition to the armoury was the weighted throwing dart, the plumbata or martiobarbulus. This gave troops missile weapons with an improved range, though carrying the penalty of a somewhat decreased penetration power. Also the more widespread indications for the incorporation of archers in javelin armed units may point to an increase in the proportion of archers in late Roman formations.
The sword remained the weapon of choice for close quarter combat, though thrusting spears, daggers and axes were also employed. From the second century AD onwards weapons with longer blades had gradually replaced shortswords in infantry service. The change in weapon type does not appear to have been linked to a drastic alteration in the tactics of the Roman heavy infantry. Troops continued to fight in close order formations using cut-and-thrust swordplay. Apart from the appearance of weapons and equipment little had changed from the days of the Roman republic.
The late Roman army is often stated to have suffered from barbarisation, a deterioriation of old standards as the result of the recruitment of large numbers of barbarians, especially Germanic tribesmen, from across the borders of the empire. In fact the recruitment of barbarians into the ranks of the late Roman army did not take place in extraordinary numbers. Recent research indicated that even in the auxilia palatina, formerly considered to be heavily barbarian in composition, only a fifth to a quarter of soldiers were of barbarian extraction. Many early imperial army units contained a higher proportion of foreigners or only recently subjected barbarians. The majority of troops in the late Roman army were therefore of provincial Roman origin.
Barbarian influence on tactics, equipment and organisation also appears to have been very limited. The longer swords used by Roman infantry soldiers from the second century AD were not a sign of changing tactics. The use of the Roman shortswords for stabbing rather than slashing has always been overemphasized in modern literature. Even the republican legionaries are explicitly described by Polybius to employ their Spanish swords for slashing as well as thrusting. The longer blades of late Roman troops were pointed and would have increased their reach in close quarter battle. The spatha was in fact not a weapon that Romans took over from Germanic barbarians, but a seperate Roman development of earlier Celtic blades. As most weapons of this type found across the borders were imports from the Roman empire it appears that the barbarians adopted a Roman weapon rather than the other way round.
The performance in battle of late Roman troops was not significantly worse than that of their early imperial counterparts. The Roman army had never been an invincible war machine. The battle at Adrianople fitted in the list of Cannae, Carrhae, the Varian disaster, Tapae and countless other defeats. Even poorly armed Judean rebels destroyed the legio XII in the early stages of the Jewish War. The late Roman army had more than a fair chance of victory against any barbarian opponent it met. Persians, Sarmatians and Germans all alike were defeated time and again.
To be completed at a later date.
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Copyright by S. van Dorst 2000