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 for military glory will ever be the vice of the most exalted characters.
And of Trajan’s successors, we are told that the policy of expansion was abandoned, starting with Hadrian:
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.
And of Antoninus:
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.
Edward Gibbon, The History of the Decline and Fall of the Roman Empire, 1.1.
Thanks, dear reader, should you ever find me, for being my gadfly.