A third ancient principle of the Roman State, that only freemen could serve in the army, was theoretically maintained,48 and though it was often practically evaded and occasionally in a crisis suspended,49 it is probable that there were never many slaves enrolled.
If we examine the means by which the army was kept up, we find that the recruits may be divided into four classes. (1) There were the numerous poor adventurers, Roman or foreign, who voluntarily offered themselves to the recruiting officer and received from him the pulveraticum (“dust-money,” or travelling expenses), the equivalent of the King’s shilling. (2) There were the recruits supplied by landed proprietors from among their serf-tenants. This was a State burden, but it fell only on the estates in certain provinces.50 (3) The son of a soldier was bound to follow his father’s profession. But this hereditary military service fell into abeyance before the time of Justinian. (4) The settlements of foreign barbarians within the Empire were another source of supply. These foreigners (gentiles), incorporated in the Empire but not enjoying the personal rights of a Roman,51 were chiefly Germans and Sarmatians, and they were organised in communities under the control of Roman officers. They are found in Gaul, where they had the special name of laeti,52 and in the Alpine districts of Italy.
The Imperial army was democratic in the sense that the humblest soldier, whatever his birth might be, might attain to the highest commands by sheer talent and capacity. The first step was promotion to the posts of centenarius and ducenarius, who discharged the duties of the old centurions and our non-commissioned officers.53 Having served in these ranks the soldier could look forward to becoming a tribune, with the command of a military unit,54 and the efficient tribune would in due course receive the rank of comes.
In order to follow the history of the fifth century intelligently and understand the difficulties of the Imperial government in dealing with the barbarian invaders it would be of particular importance to know precisely the strength of the military forces at the death of Theodosius.
The strength of the Roman military establishment at the beginning of the third century seems to have been about 300,000. It was greatly increased under Diocletian; and considerable additions were made in the course of the fourth century. The data of the Notitia dignitatum would lead to the conclusion that about A.D. 428 the total strength considerably exceeded 600,000.55 We have, however, to reckon with the probability that the legions and other military units enumerated in the Notitia were not maintained at their normal strength and in some cases may have merely existed on paper. We may conjecture that if the army once actually reached the number of 650,000 it was not after the death of Theodosius, but before the rebellions of Maximus and Eugenius, in which the losses on both sides must have considerably reduced the strength of the legions. But if we confine ourselves to the consideration of the field army, there seems no reason to doubt that in A.D. 428 it was nearly 200,000 strong. It was unequally divided between east and west, the troops assigned to the west being more numerous. In Italy there were about 24,500 infantry and 3500 cavalry.56
The military organisation of Rome, as it existed at the end of the fourth century, was to be completely changed throughout the following hundred years. We have no material for tracing the steps in the transformation; of the battles which were fought in this period not a single description has come down to us. But we shall see, when we come to the sixth century, for which we have very full information, that the military forces of the Empire were then of a different character and organised on a different system from those which were led to victory by Theodosius the Great. These changes partly depended on a change in military theory. The conquests of Rome had always been due to her infantry, the cavalry had always been subsidiary, and, down to the second half of the fourth century and the successful campaigns of Julian on the Rhine, experience had consistently confirmed the theory that battles were won by infantry and that squadrons of horse were only a useful accessory arm. The battle of Hadrianople, in which the East German horsemen rode down the legions, shook this view, and the same horsemen who had defeated Valens showed afterwards in the battles which they helped Theodosius to win, how effective might be large bodies of heavy cavalry, armed with lance and sword. The lesson was not lost on the Romans, who during the following generations had to defend their provinces against the inroads of East German horsemen, and the leading feature of the transformation of the Imperial army was the gradual degradation of the infantry until it became more or less subsidiary to the cavalry on which the generals depended more and more to win their victories. In the sixth century we shall see that the battles are often fought and won by cavalry only. It is obvious that this revolution in tactic must have reacted on the organisation and carried with it a gradual modification of the legionary system. Another tactical change was the increased importance of archery, brought about by the warfare on the eastern frontier.
Rome did not depend only on her own regular armies to protect her frontiers. She relied also on the aid of the small Federate States which lay beyond her provincial boundaries but within her sphere of influence and under her control. The system of client states goes back to the time of the Republic. The princes of these peoples were bound by a definite treaty of alliance — foedus, whence they were called foederati — to defend themselves and thereby the Empire against an external foe, and in return they received protection and were dispensed from paying tribute. In the later period with which we are concerned the treaty generally took a new form. The client prince received from the Emperor a fixed yearly sum,57 supposed to be the pay of the soldiers whom he was prepared to bring into the field. We shall meet many of these federates, such as the Abasgians and Lazi of the Caucasus, the Saracens on the Euphrates, the Ethiopians on the frontier of Egypt. It was on the basis of a contract of this kind that the Visigoths were settled south of the Danube by Theodosius the Great, and it was by similar contracts that most of the German peoples who were to dismember the western provinces would establish, in the guise of Federates, a footing on Imperial soil.
It may be added that “federation” was extended so as to facilitate and regulate the practice of purchasing immunity from foreign foes, such as the Huns and Persians, a device to which the rulers of the Empire as its strength declined were often obliged to resort. The tribute which was paid for this purpose was designated by the same name (annonae) as the subsidies which were allowed to the client princes.
While the Federate system was continued and developed, a new class of troops began to be formed in the fifth century to whom the name Federates was also applied, and who must be carefully distinguished. These troops were drawn indifferently from foreign peoples; they were paid by the government, were commanded by Roman officers, and formed a distinct section of the military establishment. We shall see that, in the course of the sixth century, these mixed Federate troops had come to be the most important and probably the most efficient soldiers in the Imperial army.
The origin of another class of fighting men who were to play a considerable part in the wars of the sixth century goes back to much the same time as that of the Federates. These were the Bucellarians, or private retainers.58 It became the practice of powerful generals, and sometimes even civilians, to form an armed retinue or private bodyguard.59 These soldiers were called bucellarii, from bucella, the military biscuit. Such private armed forces were strictly illegal, but notwithstanding Imperial prohibitions60 the practice increased, the number of retainers was limited only by the wealth of their master, and officers of subordinate rank had their private armed followers. In the sixth century Belisarius had a retinue of 7000 horse, and these private troops formed a substantial fraction of the fighting strength of the Empire. When they entered the service of their master they took an oath of loyalty to the Emperor.
If the expense of maintaining the army formed a large item in the annual budget the navy cost little. It would be almost true to say that the Empire at the period had no naval armaments. There were indeed fleets at the old naval stations which Augustus had established at Misenum and Ravenna, and another squadron (classis Venetum) was maintained at Aquileia. But it is significant that the prefects of these