But it would appear that another reason for the increase of the horsemen was even more powerful. The ascendancy of the Roman infantry over its enemies was no longer so marked as in earlier ages, and it therefore required to be more strongly supported by cavalry than had been previously necessary. The Franks, Burgundians, and Allemanni of the days of Constantine were no longer the half-armed savages of the first century, who, ‘without helm or mail, with weak shields of wicker-work, and armed only with the javelin[7],’ tried to face the embattled front of the cohort. They had now the iron-bound buckler, the pike, and the short stabbing sword (‘scramasax’), as well as the long cutting sword (‘spatha’), and the deadly ‘francisca’ or battle-axe, which, whether thrown or wielded, would penetrate Roman armour and split the Roman shield. As weapons for hand to hand combat these so far surpassed the old ‘framea,’ that the imperial infantry found it no light matter to defeat a German tribe. At the same time, the morale of the Roman army was no longer what it had once been: the corps were no longer homogeneous, and the insufficient supply of recruits was eked out by enlisting slaves and barbarians in the legions themselves, and not only among the auxiliary cohorts[8]. Though seldom wanting in courage, the troops of the fourth century had lost the self-reliance and cohesion of the old Roman infantry, and required far more careful handling on the part of the general. Few facts show this more forcibly than the proposal of the tactician Urbicius to furnish the legionaries with a large supply of portable beams and stakes, to be carried by pack-mules attached to each cohort. These were to be planted on the flanks and in the front of the legion, when there was a probability of its being attacked by hostile cavalry: behind them the Romans were to await the enemy’s onset, without any attempt to assume the offensive[9]. This proposition marks a great decay in the efficiency of the imperial foot-soldier: the troops of a previous generation would have scorned such a device, accustomed as they were to drive back with ease the assaults of the Parthian and Sarmatian ‘cataphracti.’
This tendency to deterioration on the part of the Roman infantry, and the consequent neglect of that arm by the generals of the time, were brought to a head by a disaster. The battle of Adrianople was the most fearful defeat suffered by a Roman army since Cannæ; a slaughter to which it is aptly compared by the military author Ammianus Marcellinus. The Emperor Valens, all his chief officers[10], and forty thousand men were left upon the field; indeed the army of the East was almost annihilated, and was never reorganized upon the same lines as had previously served for it.
The military importance of Adrianople was unmistakable; it was a victory of cavalry over infantry. The imperial army had developed its attack on the position of the Goths, and the two forces were hotly engaged, when suddenly a great body of horsemen charged in upon the Roman flank. It was the main strength of the Gothic cavalry, which had been foraging at a distance; receiving news of the fight it had ridden straight for the battlefield. Two of Valens’ squadrons, which covered the flank of his array, threw themselves in the way of the oncoming mass, and were ridden down and trampled under foot. Then the Goths swept down on the infantry of the left wing, rolled it up, and drove it in upon the centre. So tremendous was their impact that the legions and cohorts were pushed together in helpless confusion. Every attempt to stand firm failed, and in a few minutes left, centre, and reserve were one undistinguishable mass. Imperial guards, light troops, lancers, foederati and infantry of the line were wedged together in a press that grew closer every moment. The Roman cavalry saw that the day was lost, and rode off without another effort. Then the abandoned infantry realised the horror of their position: equally unable to deploy or to fly, they had to stand to be cut down. It was a sight such as had been seen once before at Cannæ, and was to be seen once after at Rosbecque. Men could not raise their arms to strike a blow, so closely were they packed; spears snapped right and left, their bearers being unable to lift them to a vertical position: many soldiers were stifled in the press. Into this quivering mass the Goths rode, plying lance and sword against the helpless enemy. It was not till two-thirds of the Roman army had fallen that the thinning of the ranks enabled a few thousand men to break out[11], and follow their right wing and cavalry in a headlong flight.
Such was the battle of Adrianople, the first great victory gained by that heavy cavalry which had now shown its ability to supplant the heavy infantry of Rome as the ruling power of war. During their sojourn in the steppes of South Russia the Goths, first of all Teutonic races, had become a nation of horsemen. Dwelling in the Ukraine, they had felt the influence of that land, ever the nurse of cavalry, from the day of the Scythian to that of the Tartar and Cossack. They had come to ‘consider it more honourable to fight on horse than on foot[12],’ and every chief was followed by his war-band of mounted men. Driven against their will into conflict with the empire, they found themselves face to face with the army that had so long held the world in fear. The shock came, and, probably to his own surprise, the Goth found that his stout lance and good steed would carry him through the serried ranks of the legion. He had become the arbiter of war, the lineal ancestor of all the knights of the middle ages, the inaugurator of that ascendancy of the horseman which was to endure for a thousand years.
Theodosius, on whom devolved the task of reorganizing the troops of the Eastern empire, appears to have appreciated to its fullest extent the military meaning of the fight of Adrianople. Abandoning the old Roman theory of war, he decided that the cavalry must in future compose the most important part of the imperial army. To provide himself with a sufficient force of horsemen, he was driven to a measure destined to sever all continuity between the military organization of the fourth and that of the fifth century. He did not, like Constantine, raise new corps, but began to enlist wholesale every Teutonic chief whom he could bribe to enter his service. The war-bands which followed these princes were not incorporated with the national troops; they obeyed their immediate commanders alone, and were strangers to the discipline of the Roman army. Yet to them was practically entrusted the fate of the empire; since they formed the most efficient division of the imperial forces. From the time of Theodosius the prince had to rely for the maintenance of order in the Roman world merely on the amount of loyalty which a constant stream of titles and honours could win from the commanders of the ‘Foederati.’
Only six years after Adrianople there were already 40,000 Gothic and other German horsemen serving under their own chiefs in the army of the East. The native troops sunk at once to an inferior position in the eyes of Roman generals, and the justice of their decision was verified a few years later when Theodosius’ German mercenaries won for him the two well-contested battles which crushed the usurper Magnus Maximus and his son Victor. On both those occasions, the Roman infantry of the West, those Gallic legions who had always been considered the best footmen in the world, were finally ridden down by the Teutonic cavalry who followed the standard of the legitimate emperor[13].
A picture of the state of the imperial army in the Western provinces, drawn precisely at this period, has been preserved for us in the work of Vegetius, a writer whose treatise would be of far greater value had he refrained from the attempt to identify the organization of his own day with that of the first century, by the use of the same words for entirely different things. In drawing inferences from his statements, it has also to be remembered that he frequently gives the ideal military forms of his imagination, instead of those which really existed in his day. For example, his legion is made to consist of 6000 men, while we know that in the end of the fourth century its establishment did not exceed 1500. His work is dedicated to one of the emperors who bore the name of Valentinian, probably to the second, as (in spite of Gibbon’s arguments in favour of Valentinian III) the relations of the various arms to each other and the character of their organization point to a date prior to the commencement of the fifth century.
A single fact mentioned by Vegetius gives us the date at which the continuity of the existence of the old Roman heavy infantry may be said to terminate. As might be expected, this epoch exactly corresponds with that of the similar change in the East, which followed the battle of Adrianople. ‘From the foundation of the city to the reign of the sainted Gratian,’ says the tactician, ‘the legionaries wore helmet and cuirass. But when the practice of holding frequent reviews and sham-fights ceased, these arms began to seem heavy, because the soldiers seldom put them on. They therefore begged from the emperor permission to discard first their cuirasses, and then even their helmets, and went to face the barbarians unprotected by defensive arms. In spite of the disasters which have since ensued, the infantry have not yet resumed the use of them.... And now, how can the Roman soldier expect victory, when helmless and unarmoured, and even without a shield (for the shield cannot be used in conjunction with the bow), he goes against the enemy[14]?’
Vegetius--often more of a rhetorician than a soldier--has evidently misstated the reason of this change in infantry equipment. At a time when cavalry were clothing themselves in more complete armour, it is not likely that the infantry were discarding it from mere sloth and feebleness. The real meaning of the change was that, in despair of resisting horsemen any longer by the solidity of a line of heavy infantry, the Romans had turned their attention to the use of missile weapons,--a method of resisting cavalry even more efficacious than that which they abandoned, as was to be shown a thousand years later at Cressy and Agincourt. That Vegetius’ account is also considerably exaggerated is shown by his enumeration of the legionary order of his own day, where the first rank was composed of men retaining shield, pilum, and cuirass (whom he pedantically calls ‘Principes’). The second rank was composed of archers, but wore the cuirass and carried a lance also; only the remaining half of the legion had entirely discarded armour, and given up all weapons but the bow.
Vegetius makes it evident that cavalry, though its importance was rapidly increasing, had not yet entirely supplanted infantry to such a large extent as in the Eastern Empire. Though no army can hope for success without them, and though they must always be at hand to protect the flanks, they are not, in his estimation, the most effective force. As an antiquary he feels attached to the old Roman organization, and must indeed have been somewhat behind the military experience of his day. It may, however, be remembered that the Franks and Allemanni, the chief foes against whom the Western legions had to contend, were--unlike the Goths--nearly all footmen. It was not till the time of Alaric that Rome came thoroughly to know the Gothic horsemen, whose efficiency Constantinople had already comprehended and had contrived for the moment to subsidize. In the days of Honorius, however, the Goth became the terror of Italy, as he had previously been of the Balkan peninsula. His lance and steed once more asserted their supremacy: the generalship of Stilicho, the trained bowmen and pikemen of the reorganized Roman army, the native and foederate squadrons whose array flanked the legions, were insufficient to arrest the Gothic charge. For years the conquerors rode at their will through Italy: when they quitted it, it was by their own choice, for there were no troops left in the world who could have expelled them by force.