The Vedas comprise a vast corpus of Sanskrit poetry, philosophical dialogue, myth, and ritual incantations developed and composed by Aryans over 3,500 years ago. Regarded by Hindus as the primary source of knowledge and the sacred foundation of their religion, the Vedas embody one of the worlds oldest surviving cultural traditions. The Vedic heritage embraces a multitude of texts and interpretations collected in four Vedas, commonly referred to as books of knowledge even though they have been transmitted orally. The Rig Veda is an anthology of sacred hymns; the Sama Veda features musical arrangements of hymns from the Rig Veda and other sources; the Yajur Veda abounds in prayers and sacrificial formulae used by priests; and the Atharna Veda includes incantations and spells. The Vedas also offer insight into the history of Hinduism and the early development of several artistic, scientific and philosophical concepts, such as the concept of zero.