The employment of Purohitas by kings as their substitutes in the performance of sacrificial functions is to be regarded as the beginning and the oldest form of the priesthood in India. It became the starting-point of the historically unique hierarchical order in which the sacerdotal caste occupied the supreme position in society, and the State was completely merged in the Church. Such, indeed, was the ideal of the Catholic Church in the West during the Middle Ages, but it never became an accomplished fact in Europe, as it did in India. No sooner had the priesthood become hereditary than the development of a caste system began, which has had no parallel in any other country. But during the period represented by Sudas and Vasishtha, in which the older portion of the Rigveda was composed, the priesthood was not yet hereditary, still less had the warrior and sacerdotal classes became transformed into castes among the Aryan tribes settled in the Panjab. This is confirmed by the fact that in the epic age the inhabitants of Madhyadeça or Mid-land, where the Brahmanic caste system grew up, regarded the people of the north-west as semi-barbarians. In the simple social organisation of the Vedic tribes of this region, where occupations were but little differentiated, every man was a soldier as well a civilian, much as among the Afghans of to-day. As they moved farther to the east, society became more complex, and vocations tended to become hereditary. The population being now spread over wider tracts of territory, the necessity arose for something in the nature of a standing army to repel sudden attacks or quell risings of the subject aborigines. The nucleus would have been supplied by the families of the chiefs of lesser tribes which had amalgamated under some military leader. The agricultural and industrial part of the population were thus left to follow their pursuits without interruption. Meanwhile the religious ceremonial was increasing in complexity; its success was growing more dependent on correct performance, while the preservation of the ancient hymns was becoming more urgent. The priests had, therefore, to devote all their time and energies to the carrying out of their religious duties and the handing down of the sacred tradition in their families.