During the larger part of the period of conquest which terminated in universal empire, and until the Roman army was reorganized as a mercenary body of professional troops under Caius Marius, about a hundred years before the beginning of the Christian era, every citizen except those of the lowest class was liable to military service between the ages seventeen and sixty. The older men (forty-seven to sixty years) acted as home guards or did garrison duty only, except in times of emergency, but the younger legionary might be called out for from sixteen to twenty campaigns in the field, unless earlier disabled by honorable wounds. Army life, therefore, became an educational factor of the first rank. Under the earlier (Servian) plan of enrolment citizens above a certain minimum property rating were grouped in five classes according to wealth, beginning with the richest, and if chosen served without pay and also furnished their own equipment and rations. The first class was protected by helmet, cuirass, greaves, and shield, and fought with long lance and sword. The second and third were not so completely armed, but with the first constituted the heavy infantry, arranged in three parallel lines for battle. The fourth and fifth wore no defensive armor, but were supplied with lances and javelins, or other light weapons. Each “legion” contained twenty centuries of the first class, five each of the second, third and fourth, and seven of the fifth—a total of three thousand heavy and twelve hundred light infantry, to which three hundred horsemen were added. The latter, who rode without saddle or stirrups, played only a minor part in the wars of the Republic. Soldiers were called out in the spring, and disbanded at the close of the summer campaign.