[3] the Indus Valley civilisation, which spread and flourished in the north-western part of the Indian subcontinent from 3300 to 1300 BCE, was the first major civilisation in South Asia.[4] A sophisticated and technologically advanced urban culture developed in the Mature Harappan period, from 2600 to 1900 BCE.[5] Indus Valley Civilisation was noted for developing new techniques in handicraft, carnelian products, seal carving, metallurgy, urban planning, baked brick houses, efficient drainage systems, water supply systems and clusters of large non-residential buildings.[6] This civilisation collapsed at the start of the second millennium BCE and was later followed by the Iron Age Vedic Civilisation.
In the beginning of the second millennium BCE climate change, with persistent drought, led to the abandonment of the urban centers of the Indus Valley Civilisation. Its population resettled in smaller villages, and, in the north-west, mixed with Indo-Aryan tribes, who moved into the area in several waves of Aryan migration, also driven by the effects of this climate change. The Vedic period was marked by the composition of the Vedas, large collections of hymns of some of the Aryan tribes, whose postulated religious culture, through synthesis with the preexisting religious cultures of the subcontinent, gave rise to Hinduism. The era saw the eventual emergence of Janapadas (monarchical, state-level polities), and social stratification based on caste, which created a hierarchy