This memorable war, with a very short suspension of hostilities, lasted five years; and as the emperor could exert, without control, the whole force of the state, it was terminated by the absolute submission of the barbarians. The new province of Dacia, which formed a second exception to the precept of Augustus, was about thirteen hundred miles in circumference. Its natural boundaries were the Dniester, the Theiss, or Tibiscus, the Lower Danube, and the Euxine Sea. The vestiges of a military road may still be traced from the banks of the Danube to the neighbourhood of Bender, a place famous in modern history, and the actual frontier of the Turkish and Russian empires.

Trajan was ambitious of fame; and as long as mankind shall continue to bestow more liberal applause on their destroyers than on their benefactors, the thirst of military glory will ever be the vice of the most exalted characters. The praises of Alexander, transmitted by a succession of poets and historians, had kindled a dangerous emulation in the mind of Trajan. Like him, the Roman emperor undertook an expedition against the nations of the east, but he lamented with a sigh that his advanced age scarcely left him any hopes of equalling the renown of the son of Philip. Yet the success of Trajan, however transient, was rapid and specious. The degenerate Parthians, broken by intestine discord, fled before his arms. He descended the river Tigris in triumph, from the mountains of Armenia to the Persian Gulf. He enjoyed the honour of being the first, as he was the last, of the Roman generals, who ever navigated that remote sea. His fleets ravished the coasts of Arabia; and Trajan vainly flattered himself that he was approaching towards the confines of India. Every day the astonished senate received the intelligence of new names and new nations that acknowledged his sway. They were informed that the kings of Bosphorus, Colchos, Iberia, Albania, Osrhoene, and even the Parthian monarch himself, had accepted their diadems from the hands of the emperor; that the independent tribes of the Median and Carduchian hills had implored his protection; and that the rich countries of Armenia, Mesopotamia, and Assyria, were reduced into the state of provinces. But the death of Trajan soon clouded the splendid prospect; and it was justly to be dreaded that so many distant nations would throw off the unaccustomed yoke, when they were no longer restrained by the powerful hand which had imposed it.

It was an ancient tradition that, when the Capitol was founded by one of the Roman kings, the god Terminus (who presided over boundaries, and was represented according to the fashion of that age by a large stone) alone, among all the inferior deities, refused to yield his place to Jupiter himself. A favourable inference was drawn from his obstinacy, which was interpreted by the augurs as a sure presage that the boundaries of the Roman power would never recede. During many ages, the prediction, as it is usual, contributed to its own accomplishment. But though Terminus had resisted the majesty of Jupiter, he submitted to the authority of the emperor Hadrian. The resignation of all the eastern conquests of Trajan was the first measure of his reign. He restored to the Parthians the election of an independent sovereign; withdrew the Roman garrisons from the provinces of Armenia, Mesopotamia, and Assyria; and, in compliance with the precepts of Augustus, once more established the Euphrates as the frontier of the empire. Censure, which arraigns the public actions and the private motives of princes, has ascribed to envy a conduct which might be attributed to the prudence and moderation of Hadrian. The various character of that emperor, capable, by turns, of the meanest and the most generous sentiments, may afford some colour to the suspicion. It was, however, scarcely in his power to place the superiority of his predecessor in a more conspicuous light, than by thus confessing himself unequal to the task of defending the conquests of Trajan.

The martial and ambitious spirit of Trajan formed a very singular contrast with the moderation of his successor. The restless activity of Hadrian was not less remarkable when compared with the gentle repose of Antoninus Pius. The life of the former was almost a perpetual journey; and as he possessed the various talents of the soldier, the statesman, and the scholar, he gratified his curiosity in the discharge of his duty. Careless of the difference of seasons and of climates, he marched on foot, and bareheaded, over the snows of Caledonia, and the sultry plains of the Upper Egypt; nor was there a province of the empire which, in the course of his reign, was not honoured with the presence of the monarch.7 But the tranquil life of Antoninus Pius was spent in the bosom of Italy; and, during the twenty-three years that he directed the public administration, the longest journeys of that amiable prince extended no farther than from his palace in Rome to the retirement of his Lanuvian villa.

Notwithstanding this difference in their personal conduct, the general system of Augustus was equally adopted and uniformly pursued by Hadrian and by the two Antonines. They persisted in the design of maintaining the dignity of the empire, without attempting to enlarge its limits. By every honourable expedient they invited the friendship of the barbarians; and endeavoured to convince mankind that the Roman power, raised above the temptation of conquest, was actuated only by the love of order and justice. During a long period of forty-three years their virtuous labours were crowned with success; and, if we except a few slight hostilities that served to exercise the legions of the frontier, the reigns of Hadrian and Antoninus Pius offer the fair prospect of universal peace.8 The Roman name was revered among the most remote nations of the earth. The fiercest barbarians frequently submitted their differences to the arbitration of the emperor; and we are informed by a contemporary historian that he had seen ambassadors who were refused the honour which they came to solicit, of being admitted into the rank of subjects.

The terror of the Roman arms added weight and dignity to the moderation of the emperors. They preserved peace by a constant preparation for war; and while justice regulated their conduct, they announced to the nations on their confines that they were as little disposed to endure as to offer an injury.