The Aryan Hindus, whose religions we describe in this volume[1], formed one of the Aryan or so-called Indo-European peoples. To the other peoples of this stock, Persians, Armenians, Greeks, Italians, Kelts, Teutons, Slavs, the Hindus were related closely by language, but very remotely from the point of view of their primitive religion. Into India the Aryans brought little that was retained in their religious systems. A few waning gods, the worship of ancestors, and some simple rites are common to them and their western relations; but with the exception of the Iranians (Persians), their religious connection with cis-Indic peoples is of the slightest. With the Iranians, the Hindus (that were to be) appear to have lived longest in common after the other members of the Aryan host were dispersed to west and south[2]. They stand in closer religious touch with these, their nearest neighbors, and in the time of the Rig Veda (the Hindus' earliest literature) there are traces of a connection comparatively recent between the pantheons of the two nations. According to their own, rather uncertain, testimony, the Aryans of the Rig Veda appear to have consisted of five tribal groups[3]. These groups, _janas_, Latin gens, are subdivided into _viças_, Latin vicus, and these, again, into _gr[=a]mas_. The names, however, are not employed with strictness, and _jana_, etymologically gens but politically tribus, sometimes is used as a synonym of _gr[=a]ma_.[4] Of the ten books of the Rig-Veda seven are ascribed to various priestly families. In the main, these books are rituals of song as inculcated for the same rites by different family priests and their descendants. Besides these there are books which are ascribed to no family, and consist, in part, of more general material. The distinction of priestly family-books was one, possibly, coextensive with political demarcation. Each of the family-books represents a priestly family, but it may represent, also, a political family. In at least one case it represents a political body.[5]