With regard to Egypt, Africa, and Spain, as they were far removed from any important scene of war, a single legion maintained the domestic tranquillity of each of those great provinces.
Even Italy was not left destitute of a military force.

Above twenty thousand chosen soldiers, distinguished by the titles of City Cohorts and Praetorian Guards, watched over the safety of the monarch and the capital.

As the authors of almost every revolution that distracted the empire, the Praetorians will, very soon, and very loudly, demand our attention; but, in their arms and institutions, we cannot find any circumstance which discriminated them from the legions, unless it were a more splendid appearance, and a less rigid discipline.
The navy maintained by the emperors might seem inadequate to their greatness; but it was fully sufficient for every useful purpose of government.

The ambition of the Romans was confined to the land; nor was that warlike people ever actuated by the enterprising spirit which had prompted the navigators of Tyre, of Carthage, and even of Marseilles, to enlarge the bounds of the world, and to explore the most remote coasts of the ocean.

To the Romans the ocean remained an object of terror rather than of curiosity; the whole extent of the Mediterranean, after the destruction of Carthage, and the extirpation of the pirates, was included within their provinces.