Owing to these causes, the three main classes of Aryan society became more and more separated. But how were they transformed into castes or social strata divided from one another by the impassable barriers of heredity and the prohibition of intermarrying or eating together? This rigid mutual exclusiveness must have started, in the first instance, from the treatment of the conquered aborigines, who, on accepting the Aryan belief, were suffered to form a part of the Aryan polity in the capacity of a servile class. The gulf between the two races need not have been wider than that which at the present day, in the United States, divides the whites from the negroes. When the latter are described as men of "colour," the identical term is used which, in India, came to mean "caste." Having become hereditary, the sacerdotal class succeeded in securing a position of sanctity and inviolability which raised them above the rest of the Aryans as the latter were raised above the Dasas. When their supremacy was established, they proceeded to organise the remaining classes in the state on similar lines of exclusiveness. To the time when the system of the three Aryan castes, with the Çudras added as a fourth, already existed in its fundamental principles, belong the greater part of the independent portions of the Yajurveda, a considerable part of the Atharva-veda (most of books viii. to xiii.), but of the Rigveda, besides the one (x. 90) which distinctly refers to the four castes by name, only a few of the latest hymns of the first, eighth, and tenth books. The word brahmana, the regular name for "man of the first caste," is still rare in the Rigveda, occurring only eight times, while brahman, which simply means sage or officiating priest, is found forty-six times. We may now pass on to sketch rapidly the social conditions which prevailed in the period of the Rigveda. The family, in which such relationships as a wife's brother and a husband's brother or sister had special names, was clearly the foundation of society. The father was at its head as "lord of the house" (grihapati). Permission to marry a daughter was asked from him by the suitor through the mediation of an intimate friend. The wedding was celebrated in the house of the bride's parents, whither the bridegroom, his relatives, and friends came in procession. Here they were entertained with the flesh of cows slain in honour of the occasion. Here, too, the bridegroom took the bride's hand and led her round the nuptial fire. The Atharva-veda adds that he set down a stone on the ground, asking the bride to step upon it for the obtainment of offspring. On the conclusion of the wedding festivities, the bride, anointed and in festal array, mounted with her husband a car adorned with red flowers and drawn by two white bulls. On this she was conducted in procession to her new home. The main features of this nuptial ceremony of 3000 years ago still survive in India.