8. The legion consisted of three lines or battalions; the _Hasta'ti_, the _Prin'cipes_, and the _Tria'rii_; there were besides two classes, which we may likewise call battalions, the _Rora'rii_, or _Velites_, consisting of light armed troops, and the _Accen'si_, or supernumeraries, who were ready to supply the place of those that fell. Each of the two first battalions contained fifteen manip'uli, consisting of sixty privates, commanded by two centurions, and having each a separate standard (_vexil'lum_) borne by one of the privates called Vexilla'rius; the manip'uli in the other battalions were fewer in number, but contained a greater portion of men; so that, in round numbers, nine hundred men may be allowed to each battalion, exclusive of officers. If the officers and the troop of three hundred cavalry be taken into account, we shall find that the legion, as originally constituted, contained about five thousand men. The Romans, however, did not always observe these exact proportions, and the number of soldiers in a legion varied at different times of their history.[1] 9. A cohort was formed by taking a manipulus from each of the battalions; more frequently two manipuli were taken, and the cohort then contained six hundred men. The cavalry were divided into tur'mae, consisting each of thirty men. 10. A battle was usually commenced by the light troops, who skirmished with missile weapons; the hasta'ti then advanced to the charge, and if defeated, fell back on the prin'cipes; if the enemy proved still superior, the two front lines retired to the ranks of the tria'rii, which being composed of veteran troops, generally turned the scale. But this order was not always observed; the number of divisions in the legion made it extremely flexible, and the commander-in-chief could always adapt the form of his line to circumstances. 11. The levies of troops were made in the Cam'pus Mar'tius, by the tribunes appointed to command the legions. The tribes which were to supply soldiers were determined by lot, and as each came forward, the tribunes, in their turn, selected such as seemed best fitted for war. Four legions was most commonly the number in an army. When the selected individuals had been enrolled as soldiers, one was chosen from each legion to take the military oath of obedience to the generals; the other soldiers swore in succession, to observe the oath taken by their foreman. 12. Such was the sacredness of this obligation, that even in the midst of the political contests by which the city was distracted, the soldiers, though eager to secure the freedom of their country, would not attempt to gain it by mutiny against their commanders. On this account the senate frequently declared war, and ordered a levy as an expedient to prevent the enactment of a popular law, and were of course opposed by the tribunes of the people.