Mention is often made in the Rigveda of the sapta sindhavah, or "seven rivers," which in one passage at least is synonymous with the country inhabited by the Aryan Indians. It is interesting to note that the same expression hapta hindu occurs in the Avesta, though it is there restricted to mean only that part of the Indian territory which lay in Eastern Kabulistan. If "seven" is here intended for a definite number, the "seven rivers" must originally have meant the Kabul, the Indus, and the five rivers of the Panjab, though later the Sarasvati may have been substituted for the Kabul. For the Sarasvati is the sacred river of the Rigveda, more frequently mentioned, generally as a goddess, and lauded with more fervour than any other stream. The poet's descriptions are often only applicable to a large river. Hence Roth and other distinguished scholars concluded that Sarasvati is generally used by the poets of the Rigveda simply as a sacred designation of the Indus. On the other hand, the name in a few passages undoubtedly means the small river midway between the Sutlej and the Jumna, which at a later period formed, with the Drishadvati, the eastern boundary of the sacred region called Brahmavarta, lying to the south of Ambala, and commencing some sixty miles south of Simla. This small river now loses itself in the sands of the desert, but the evidence of ancient river-beds appears to favour the conclusion that it was originally a tributary of the Çutudri (Sutlej). It is therefore not improbable that in Vedic times it reached the sea, and was considerably larger than it is now. Considering, too, the special sanctity which it had already acquired, the laudations supposed to be compatible only with the magnitude of the Indus may not have seemed too exaggerated when applied to the lesser stream. It is to be noted that the Drishadvati, the "stony" (now Ghogra or Ghugger), in the only passage in which the name occurs in the Rigveda, is associated with the Sarasvati, Agni being invoked to flame on the banks of these rivers. This is perhaps an indication that even in the age of the Rigveda the most easterly limit of the Indus river system had already acquired a certain sanctity as the region in which the sacrificial ritual and the art of sacred poetry were practised in the greatest perfection. There are indications showing that by the end at least of the Rigvedic period some of the Aryan invaders had passed beyond this region and had reached the western limit of the Gangetic river system. For the Yamuna (now Jumna), the most westerly tributary of the Ganges in the north, is mentioned in three passages, two of which prove that the Aryan settlements already extended to its banks. The Ganges itself is already known, for its name is mentioned directly in one passage of the Rigveda and indirectly in another. It is, however, a noteworthy fact that the name of the Ganges is not to be found in any of the other Vedas.