His generals, in the early part of his reign, attempted the reduction of Ethiopia 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 un-warlike natives of those sequestered regions. The northern countries of Europe scarcely deserved the expense and labor 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. 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 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.