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 fleets, which were probably very small, were under the control of the Master of Soldiers in Italy.61 There was no independent naval command. In the east we find no mention of fleets or naval stations62 with the exception of the small flotillas which patrolled the Lower Danube under the direction of military commanders on that frontier. For centuries the Mediterranean had been a Roman lake, and it was natural that the navy should come to be held as an almost negligible instrument of war. In the third century it had been neglected so far as even to be inadequate to the duty of policing the waters and protecting the coasts against piracy. An amazing episode in the reign of Probus illustrates its inefficiency.63 A party of Franks, settled on the shores of the Black Sea, seized some vessels, sailed through the Propontis, plundered Carthage, Syracuse, and other cities, and then passing into the Atlantic safely reached the mouths of the Rhine. Yet in the contest between Constantine and Licinius navies played a decisive part, and the two adversaries seemed to have found many useful vessels in the ports of Greece, Syria, Egypt, and Asia Minor. The fleet of Licinius numbered 350 ships and that of Constantine 200, some of which he built for the occasion. It is not clear what the status of these ships was. In the fifth century the Empire was to feel the want of an efficient navy, when the Mediterranean ceased to be an entirely Roman sea and a new German power in Africa contested the supremacy of its waters. But the failures and defeats which marked the struggle with the vandals did not impress the government of Constantinople with the need of building up a strong navy. The sea forces continued to be regarded as subsidiary, and in overseas expeditions the fleets which convoyed the transports were never placed under an independent naval command. Not until the seventh century, when the Empire had to fight for its very existence with an enemy more formidable than the Vandals, was a naval establishment effectively organised and an independent Ministry of Marine created.
§ 3. The Financial System
There are three things which it is important to know about the finances of the Empire. The first is, the sources of revenue, and how they were collected; the second is the total amount of the revenue; the third is the total amount of the normal expenditure. As to the first we are fairly well informed; we know a good deal, from first-hand sources, about the system of taxation and the financial machinery. As to the second and third we are in the dark. No official figures as to the annual budget at any period of the later Roman Empire have been preserved, and all attempts to calculate the total of either income or outgoings are guess work, and are based on assumptions which may or may not be true. The utmost that can be done is to fix a minimum.
The financial, like every other department of administration under the autocracy, differed in its leading features from that of the Principate. In raising the revenue the ideal aimed at was equalisation and uniformity; to treat the whole Empire alike, to abolish privileges and immunities. Italy, which had always been free from the burdens borne by the provinces, was largely deprived of this favoured position by the policy of Diocletian.64 The ideal was not entirely attained; some anomalies and differences survived; but on the whole, uniformity in taxation is the striking characteristic of the new system in contrast with the old. Another capital difference had been gradually brought about. The device of committing the collection of the revenue to middlemen, the publicans, who realised profits altogether disproportionate to their services, was superseded partly by the direct collection of the taxes by Imperial officials, partly through the agency of the local magistracies of the towns. Moreover, when we survey the sources of revenue at the end of the fourth century, we find that many of the old imposts of the Principate have disappeared, that new taxes have taken their place, and that the modes of assessment have been changed.
The most important and productive source of revenue was the tax on land and agricultural labour. This tax consisted of two distinct parts, the ground tax proper, which represented the old tributum imposed on conquered territories, and the annona. The tribute was paid only by those communities and in those districts which had always been liable; it was
