The hostilities of the barbarians provoked the resentment of that philosophic monarch, and, in the prosecution of a just defence, Marcus and his generals obtained many signal victories, both on the Euphrates and on the Danube.

The military establishment of the Roman empire, which thus assured either its tranquillity or success, will now become the proper and important object of our attention.
In the purer ages of the commonwealth, the use of arms was reserved for those ranks of citizens who had a country to love, a property to defend, and some share in enacting those laws, which it was their interest as well as duty to maintain.

But in proportion as the public freedom was lost in extent of conquest, war was gradually improved into an art, and degraded into a trade.

The legions themselves, even at the time when they were recruited in the most distant provinces, were supposed to consist of Roman citizens.

That distinction was generally considered, either as a legal qualification or as a proper recompense for the soldier; but a more serious regard was paid to the essential merit of age, strength, and military stature.