The cavalry, without which the force of the legion would have remained imperfect, was divided into ten troops or squadrons; the first, as the companion of the first cohort, consisted of an hundred and thirty-two men; whilst each of the other nine amounted only to sixty-six. The entire establishment formed a regiment, if we may use the modern expression, of seven hundred and twenty-six horse, naturally connected with its respective legion, but occasionally separated to act in the line, and to compose a part of the wings of the army.Ref. 092 The cavalry of the emperors was no longer composed, like that of the ancient republic, of the noblest youths of Rome and Italy, who, by performing their military service on horseback, prepared themselves for the offices of senator and consul; and solicited, by deeds of valour, the future suffrages of their countrymen.Ref. 093 Since the alteration of manners and government, the most wealthy of the equestrian order were engaged in the administration of justice, and of the revenue;Ref. 094 and whenever they embraced the profession of arms, they were immediately intrusted with a troop of horse, or a cohort of foot.Ref. 095 Trajan and Hadrian formed their cavalry from the same provinces, and the same class of their subjects, which recruited the ranks of the legion. The horses were bred, for the most part, in Spain or Cappadocia. The Roman troopers despised the complete armour with which the cavalry of the East was encumbered. Their more useful arms consisted in a helmet, an oblong shield, light boots, and a coat of mail. A javelin, and a long broad sword, were their principal weapons of offence. The use of lances and of iron maces they seem to have borrowed from the barbarians.Ref. 096
The safety and honour of the empire was principally intrusted to the legions, but the policy of Rome condescended to adopt every useful instrument of war. Considerable levies were regularly made among the provincials, who had not yet deserved the honourable distinction of Romans. Many dependent princes and communities, dispersed round the frontiers, were permitted, for a while, to hold their freedom and security by the tenure of military service.Ref. 097 Even select troops of hostile barbarians were frequently compelled or persuaded to consume their dangerous valour in remote climates, and for the benefit of the state.Ref. 098 All these were included under the general name of auxiliaries; and howsoever they might vary according to the difference of times and circumstances, their numbers were seldom much inferior to those of the legions themselves.Ref. 099 Among the auxiliaries, the bravest and most faithful bands were placed under the command of prefects and centurions, and severely trained in the arts of Roman discipline; but the far greater part retained those arms, to which the nature of their country, or their early habits of life, more peculiarly adapted them. By this institution, each legion, to whom a certain proportion of auxiliaries was allotted, contained within itself every species of lighter troops, and of missile weapons; and was capable of encountering every nation with the advantages of its respective arms and discipline.Ref. 100 Nor was the legion destitute of what, in modern language, would be styled a train of artillery. It consisted in ten military engines of the largest, and fifty-five of a smaller size; but all of which, either in an oblique or horizontal manner, discharged stones and darts with irresistible violence.Ref. 101
The camp of a Roman legion presented the appearance of a fortified city.Ref. 102 As soon as the space was marked out, the pioneers carefully levelled the ground, and removed every impediment that might interrupt its perfect regularity. Its form was an exact quadrangle; and we may calculate, that a square of about seven hundred yards was sufficient for the encampment of twenty thousand Romans; though a similar number of our own troops would expose to the enemy a front of more than treble that extent. In the midst of the camp, the prætorium, or general’s quarters, rose above the others; the cavalry, the infantry, and the auxiliaries occupied their respective stations; the streets were broad and perfectly straight, and a vacant space of two hundred feet was left on all sides, between the tents and the rampart. The rampart itself was usually twelve feet high, armed with a line of strong and intricate palisades, and defended by a ditch of twelve feet in depth as well as in breadth. This important labour was performed by the hands of the legionaries themselves; to whom the use of the spade and the pick-axe was no less familiar than that of the sword or pilum. Active valour may often be the present of nature; but such patient diligence can be the fruit only of habit and discipline.Ref. 103
Whenever the trumpet gave the signal of departure, the camp was almost instantly broken up, and the troops fell into their ranks without delay or confusion. Besides their arms, which the legionaries scarcely considered as an encumbrance, they were laden with their kitchen furniture, the instruments of fortification, and the provision of many days.Ref. 104 Under this weight, which would oppress the delicacy of a modern soldier, they were trained by a regular step to advance, in about six hours, near twenty miles.Ref. 105 On the appearance of an enemy, they threw aside their baggage, and, by easy and rapid evolutions, converted the column of march into an order of battle.Ref. 106 The slingers and archers skirmished in the front; the auxiliaries formed the first line, and were seconded or sustained by the strength of the legions; the cavalry covered the flanks, and the military engines were placed in the rear.
Such were the arts of war, by which the Roman emperors defended their extensive conquests, and preserved a military spirit, at a time when every other virtue was oppressed by luxury and despotism. If, in the consideration of their armies, we pass from their discipline to their numbers, we shall not find it easy to define them with any tolerable accuracy. We may compute, however, that the legion, which was itself a body of six thousand eight hundred and thirty-one Romans, might, with its attendant auxiliaries, amount to about twelve thousand five hundred men. The peace establishment of Hadrian and his successors was composed of no less than thirty of these formidable brigades; and most probably formed a standing force of three hundred and seventy-five thousand men. Instead of being confined within the walls of fortified cities, which the Romans considered as the refuge of weakness or pusillanimity, the legions were encamped on the banks of the great rivers, and along the frontiers of the barbarians. As their stations, for the most part, remained fixed and permanent, we may venture to describe the distribution of the troops. Three legions were sufficient for Britain. The principal strength lay upon the Rhine and Danube, and consisted of sixteen legions, in the following proportions: two in the Lower, and three in the Upper Germany; one in Rhætia, one in Noricum, four in Pannonia, three in Mæsia, and two in Dacia. The defence of the Euphrates was intrusted to eight legions, six of whom were planted in Syria, and the other two in Cappadocia. With regard to Egypt, Africa, and Spain, as they were far removed from any important scene of war, a single legion maintained the domestic tranquillity of each of those great provinces. Even Italy was not left destitute of a military force. Above twenty thousand chosen soldiers, distinguished by the titles of City Cohorts and Prætorian Guards, watched over the safety of the monarch and the capital. As the authors of almost every revolution that distracted the empire, the Prætorians will very soon and very loudly demand our attention; but, in their arms and institutions, we cannot find any circumstance which discriminated them from the legions, unless it were a more splendid appearance, and a less rigid discipline.Ref. 107
The navy maintained by the emperors might seem inadequate to their greatness; but it was fully sufficient for every useful purpose of government. The ambition of the Romans was confined to the land; nor was that warlike people ever actuated by the enterprising spirit which had prompted the navigators of Tyre, of Carthage, and even of Marseilles, to enlarge the bounds of the world, and to explore the most remote coasts of the ocean. To the Romans the ocean remained an object of terror rather than of curiosity;Ref. 108 the whole extent of the Mediterranean, after the destruction of Carthage and the extirpation of the pirates, was included within their provinces. The policy of the emperors was directed only to preserve the peaceful dominion of that sea, and to protect the commerce of their subjects. With these moderate views, Augustus stationed two permanent fleets in the most convenient ports of Italy, the one at Ravenna, on the Adriatic, the other at Misenum, in the bay of Naples.