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 Caesars 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 valor 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.
The only accession which the Roman empire received, during the first century of the Christian AEra, was the province of Britain.

In this single instance, the successors of Caesar 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; 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, 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.