It is the design of this and of the two succeeding chapters, to describe the prosperous condition of their empire; and afterwards, from the death of Marcus Antoninus, to deduce the most important circumstances of its decline and fall: a revolution which will ever be remembered, and is still felt by the nations of the earth.

The principal conquests of the Romans were achieved under the republic; and the emperors, for the most part, were satisfied with preserving those dominions which had been acquired by the policy of the senate, the active emulation of the consuls, and the martial enthusiasm of the people. The seven first centuries were filled with a rapid succession of triumphs; but it was reserved for Augustus to relinquish the ambitious design of subduing the whole earth, and to introduce a spirit of moderation into the public councils. Inclined to peace by his temper and situation, it was easy for him to discover that Rome, in her present exalted situation, had much less to hope than to fear from the chance of arms; and that, in the prosecution of remote wars, the undertaking became every day more difficult, the event more doubtful, and the possession more precarious and less beneficial. The experience of Augustus added weight to these salutary reflections, and effectually convinced him that, by the prudent vigour of his counsels, it would be easy to secure every concession which the safety or the dignity of Rome might require from the most formidable barbarians. Instead of exposing his person and his legions to the arrows of the Parthians, he obtained, by an honourable treaty, the restitution of the standards and prisoners which had been taken in the defeat of Crassus.

His generals, in the early part of his reign, attempted the reduction of Æthiopia and Arabia Felix. They marched near a thousand miles to the south of the tropic; but the heat of the climate soon repelled the invaders and protected the unwarlike natives of those sequestered regions.1 The northern countries of Europe scarcely deserved the expense and labour of conquest. The forests and morasses of Germany were filled with a hardy race of barbarians, who despised life when it was separated from freedom; and though, on the first attack, they seemed to yield to the weight of the Roman power, they soon, by a signal act of despair, regained their independence, and reminded Augustus of the vicissitude of fortune.2 On the death of that emperor his testament was publicly read in the senate. He bequeathed, as a valuable legacy to his successors, the advice of confining the empire within those limits which nature seemed to have placed as its permanent bulwarks and boundaries; on the west the Atlantic Ocean; the Rhine and Danube on the north; the Euphrates on the east; and towards the south the sandy deserts of Arabia and Africa.

Happily for the repose of mankind, the moderate system recommended by the wisdom of Augustus was adopted by the fears and vices of his immediate successors. Engaged in the pursuit of pleasure or in the exercise of tyranny, the first Cæsars seldom showed themselves to the armies, or to the provinces; nor were they disposed to suffer that those triumphs which their indolence neglected should be usurped by the conduct and valour of their lieutenants. The military fame of a subject was considered as an insolent invasion of the Imperial prerogative; and it became the duty, as well as interest, of every Roman general, to guard the frontiers intrusted to his care, without aspiring to conquests which might have proved no less fatal to himself than to the vanquished barbarians.3

The only accession which the Roman empire received during the first century of the Christian æra was the province of Britain. In this single instance the successors of Cæsar and Augustus were persuaded to follow the example of the former, rather than the precept of the latter. The proximity of its situation to the coast of Gaul seemed to invite their arms; the pleasing, though doubtful, intelligence of a pearl fishery attracted their avarice;4 and as Britain was viewed in the light of a distinct and insulated world, the conquest scarcely formed any exception to the general system of continental measures. After a war of about forty years, undertaken by the most stupid,5 maintained by the most dissolute, and terminated by the most timid of all the emperors, the far greater part of the island submitted to the Roman yoke. The various tribes of Britons possessed valour without conduct, and the love of freedom without the spirit of union. They took up arms with savage fierceness, they laid them down, or turned them against each other with wild inconstancy; and while they fought singly, they were successively subdued. Neither the fortitude of Caractacus, nor the despair of Boadicea, nor the fanaticism of the Druids, could avert the slavery of their country, or resist the steady progress of the Imperial generals, who maintained the national glory, when the throne was disgraced by the weakest or the most vicious of mankind. At the very time when Domitian, confined to his palace, felt the terrors which he inspired, his legions, under the command of the virtuous Agricola, defeated the collected force of the Caledonians at the foot of the Grampian hills; and his fleets, venturing to explore an unknown and dangerous navigation, displayed the Roman arms round every part of the island. The conquest of Britain was considered as already achieved; and it was the design of Agricola to complete and ensure his success by the easy reduction of Ireland, for which, in his opinion, one legion and a few auxiliaries were sufficient.6 The western isle might be improved into a valuable possession, and the Britons would wear their chains with the less reluctance, if the prospect and example of freedom was on every side removed from before their eyes.

But the superior merit of Agricola soon occasioned his removal from the government of Britain; and for ever disappointed this rational, though extensive, scheme of conquest. Before his departure the prudent general had provided for security as well as for dominion. He had observed that the island is almost divided into two unequal parts by the opposite gulfs or, as they are now called, the Friths of Scotland. Across the narrow interval of about forty miles he had drawn a line of military stations, which was afterwards fortified, in the reign of Antoninus Pius, by a turf rampart, erected on foundations of stone. This wall of Antoninus, at a small distance beyond the modern cities of Edinburgh and Glasgow, was fixed as the limit of the Roman province. The native Caledonians preserved, in the northern extremity of the island, their wild independence, for which they were not less indebted to their poverty than to their valour. Their incursions were frequently repelled and chastised; but their country was never subdued. The masters of the fairest and most wealthy climates of the globe turned with contempt from gloomy hills assailed by the winter tempest, from lakes concealed in a blue mist, and from cold and lonely heaths, over which the deer of the forest were chased by a troop of naked barbarians.

Such was the state of the Roman frontiers, and such the maxims of Imperial policy, from the death of Augustus to the accession of Trajan. That virtuous and active prince had received the education of a soldier, and possessed the talents of a general. The peaceful system of his predecessors was interrupted by scenes of war and conquest; and the legions, after a long interval, beheld a military emperor at their head. The first exploits of Trajan were against the Dacians, the most warlike of men, who dwelt beyond the Danube, and who, during the reign of Domitian, had insulted, with impunity, the majesty of Rome. To the strength and fierceness of barbarians they added a contempt for life, which was derived from a warm persuasion of the immortality and transmigration of the soul. Decebalus, the Dacian king, approved himself a rival not unworthy of Trajan; nor did he despair of his own and the public fortune, till, by the confession of his enemies, he had exhausted every resource both of valour and policy.