Yoga was introduced by Indian Ascetic. Ascetic practices ("tapas") are referenced in the (900 to 500 BC), early commentaries on the Vedas. Several seals discovered at Indus Valley Civilization (~3300–1700 B.C.) sites in Pakistan depict figures in positions resembling a common yoga or meditation pose. The pose shows "a form of ritual discipline, suggesting a precursor of yoga", according to archaeologist Gregory Possehl. Scholars think there must be some type of connection between the Indus Valley seals and later yoga and meditation practices, though there is no conclusive evidence.