The Vedas are the scriptures derived from the Vedic period (c.1500–700bc) following the migration of Aryan people into the Indus valley. The four chief collections are the Rig-Veda, or book of prayers and hymns, the Yajur-Veda, or book of sacrificial formulae, the Sama-Veda or book of chants, and the Athar-Veda, a book of magical spells and philosophical speculation. The most famous text is the Rig-Veda (verses of wisdom). The philosophical component of the Vedas is mainly contained in the concluding sections or explanations, known as the Upanishads.