As the Upanishads were a development of the speculative side of the Brahmanas and constituted the textbooks of Vedic dogma, so the Çrauta Sutras form the continuation of their ritual side, though they are not, like the Upanishads, regarded as a part of revelation. A sacred character was never attributed to them, probably because they were felt to be treatises compiled, with the help of oral priestly tradition, from the contents of the Brahmanas solely to meet practical needs. The oldest of them seem to go back to about the time when Buddhism came into being. Indeed it is quite possible that the rise of the rival religion gave the first impetus to the composition of systematic manuals of Brahmanic worship. The Buddhists in their turn must have come to regard Sutras as the type of treatise best adapted for the expression of religious doctrine, for the earliest Pali texts are works of this character. The term Kalpa Sutra is used to designate the whole body of Sutras concerned with religion which belonged to a particular Vedic school. Where such a complete collection has been preserved, the Çrauta Sutra forms its first and most extensive portion. To the Rigveda belong the Çrauta manuals of two Sutra schools (charanas), the Çankhayanas and the Açvalayanas, the former of whom were in later times settled in Northern Gujarat, the latter in the South between the Godavari and the Krishna. The ritual is described in much the same order by both, but the account of the great royal sacrifices is much more detailed in the Çankhayana Çrauta Sutra. The latter, which is closely connected with the Çankhayana Brahmana, seems to be the older of the two, on the ground both of its matter and of its style, which in many parts resembles that of the Brahmanas. It consists of eighteen books, the last two of which were added later, and correspond to the first two books of the Kaushitaki Aranyaka. The Çrauta Sutra of Açvalayana, which consists of twelve books, is related to the Aitareya Brahmana. Açvalayana is also known as the author of the fourth book of the Aitareya Aranyaka, and was according to tradition the pupil of Çaunaka. Three Çrauta Sutras to the Samaveda have been preserved. The oldest, that of Maçaka, also called Arsheya-kalpa, is nothing more than an enumeration of the prayers belonging to the various ceremonies of the Soma sacrifice in the order of the Panchavimça Brahmana. The Çrauta Sutra composed by Latyayana, became the accepted manual of the Kauthuma school. This Sutra, like that of Maçaka, which it quotes, is closely connected with the Panchavimça Brahmana. The Çrauta Sutra of Drahyayana, which differs but little from that of Latyayana, belongs to the Ranayaniya branch of the Samaveda.