The Vedic literature consists of four Vedas, namely: Rig Veda, Sama Veda, Yajur Veda, and Atharva Veda. The mantra text of each of the Vedas is called Samhita. They are the prose texts that explain the hymns in the Vedas and are also the classification of Sanskrit texts that are embedded within each Veda, incorporating myths and legends to explain and instruct Brahmins on the performance of Vedic rituals. In addition to explaining the symbolism and meaning of the Samhitas, Brahmana literature also expounds scientific knowledge of the Vedic Period, including observational astronomy and, particularly in relation to altar construction, geometry. Divergent in nature, some Brahmanas also contain mystical and philosophical material that constitutes Aranyakas and Upanishads.