The safety and honor of the empire was principally intrusted to the legions, but the policy of Rome condescended to adopt every useful instrument of war. Considerable levies were regularly made among the provincials, who had not yet deserved the honorable distinction of Romans. Many dependent princes and communities, dispersed round the frontiers, were permitted, for a while, to hold their freedom and security by the tenure of military service. Even select troops of hostile barbarians were frequently compelled or persuaded to consume their dangerous valor in remote climates, and for the benefit of the state. All these were included under the general name of auxiliaries; and howsoever they might vary according to the difference of times and circumstances, their numbers were seldom much inferior to those of the legions themselves. Among the auxiliaries, the bravest and most faithful bands were placed under the command of præfects and centurions, and severely trained in the arts of Roman discipline; but the far greater part retained those arms, to which the nature of their country, or their early habits of life, more peculiarly adapted them. By this institution, each legion, to whom a certain proportion of auxiliaries was allotted, contained within itself every species of lighter troops, and of missile weapons; and was capable of encountering every nation, with the advantages of its respective arms and discipline. Nor was the legion destitute of what, in modern language, would be styled a train of artillery. It consisted in ten military engines of the largest, and fifty-five of a smaller size; but all of which, either in an oblique or horizontal manner, discharged stones and darts with irresistible violence. Chapter I: The Extent Of The Empire In The Age Of The Antoninies.—Part III.