The practice of yoga has been thought to date back to pre-vedic Indian traditions; possibly in the Indus valley civilization around 3000 BCE. Yoga is mentioned in the Rigveda and referenced in the Upanishads,. Although, yoga most likely developed as a systematic study around the 5th centuries.
Ascetic practices (tapas), concentration and bodily postures used by Vedic priests to conduct yajna (sacrifice), might have been precursors to yoga.
Early Samhitas also contain references to other group ascetics such as munis, the keśin, and vratyas. Techniques for controlling breath and vital energies are mentioned in the Brahmanas.