One of the chief occupations of the Vedic Indians was of course warfare. They fought either on foot or on chariots. The latter had two occupants, the fighter and the driver. This was still the case in the Mahabharata, where we find Krishna acting as charioteer to Arjuna. Cavalry is nowhere mentioned, and probably came into use at a considerably later period. By the time of Alexander's invasion, however, it formed one of the regular four divisions of the Indian army. There are some indications that riding on horseback was at least known to the Rigveda, and distinct references to it occur in the Atharva- and the Yajur-vedas. The Vedic warriors were protected with coats of mail and helmets of metal. The principal weapons were the bow and arrow, the latter being tipped with poisoned horn or with a metal point. Spears and axes are also frequently mentioned. The principal means of livelihood to the Vedic Indian was cattle-breeding. His great desire was to possess large herds; and in the numerous prayers for protection, health, and prosperity, cattle are nearly always mentioned first. The Vedic Aryans were, however, not merely a pastoral people. They had brought with them from beyond the valleys of Afghanistan at least a primitive knowledge of agriculture, as is shown by the Indians and Iranians having such terms as "to plough" (krish) in common. This had, indeed, by the time of the Rigveda, become an industry second only to cattle-breeding in importance. The plough, which we learn from the Atharva-veda had a metal share, was used for making furrows in the fields, and was drawn by bulls. When the earth was thus prepared, seed was strewn over the soil. Irrigation seems not to have been unknown, as dug-out channels for water are mentioned. When ripe, the corn (yava) was cut with a sickle. It was then laid in bundles on the threshing-floor, where it was threshed out and finally sifted by winnowing. Though the Vedic Indians were already a pastoral and agricultural people, they still practised hunting to a considerable extent. The hunter pursued his game with bow and arrow, or used traps and snares. Birds were usually caught with toils or nets spread on the ground. Lions were taken in snares, antelopes secured in pits, and boars hunted with dogs. Navigation in Rigvedic times was, as we have already seen, limited to the crossing of rivers. The boats (called nau-s, Greek nau-s) were propelled by what were doubtless paddles (aritra), and must have been of the most primitive type, probably dug-out tree-trunks. No mention is made of rudder or anchor, masts, or sails. Trade in those days consisted in barter, the cow being the pecuniary standard by which the value of everything was measured. The transition to coinage was made by the use of gold ornaments and jewelry as a form of reward or payment, as was the case among the ancient Germans. Thus nishka, which in the Rigveda means a necklet, in later times became the name of a coin.