When the chariot gave way to the horseback rider is not definitely known; at all events the change seems to have taken place under Hellenic influence, and could hardly therefore have been earlier than the beginning of the seventh century B.C.[439] The idea of the sources is that there came to be three troops of horsemen, furnished by the tribes,[440] as well as three regiments of foot, that before Servius the number of troops of horse was doubled, and that the six troops thus formed were named accordingly after the tribes Ramnenses, Titienses, and Lucerenses priores and posteriores respectively.[441] The priores had each two horses, the posteriores one.[442] Hence the essential difference between these divisions was in rank and wealth rather than in the relative time of their institution. Long after Servius both divisions continued to be patrician.[443] As the centuriate organization of Servius applied to the infantry, the cavalry remained little affected by it. The six troops with their old names survived, and eventually became a part of the comitia centuriata. In the military sphere, however, the troop no longer retained its identity; but the whole body was divided into twenty turmae, each composed of three decuries commanded by decurions.[444] When with the institution of the republic the phalanx was split into two legions, ten turmae of cavalry were assigned to each legion.[445] As in historical time the number of horsemen to a legion did not exceed 300,[446] and as we have no reason to suppose that at an earlier period this arm of the service was proportionally stronger, we may conclude that in the Servian phalanx, or double legion, the number did not exceed 600. From the foregoing discussion it appears clear that the Servian military system rested upon a division of the citizens into four groups, closely corresponding to the Athenian census divisions: (1) the equites priores, like the pentacosiomedimni, (2) the equites posteriores, like the hippeis,[447] (3) the classis, like the zeugitae, (4) the light troops infra classem, like the thetes. The distinction between priores and posteriores rested not upon an assessment but upon a less precise difference in wealth, whether determined by the individual concerned or by the state we cannot know; it represented, too, a gradation of nobility. The distinction between the knights and the classici was one of rank; that between the classis and the soldiers infra classem was alone determined by the census. III. _The Development of the Five Post-Servian Military Divisions on the Basis of Census Ratings_