Vedic architecture originated after the decline of the Indus Valley civilization. The Aryans who entered India around 1500 BC established settlements and built villages. Their early structures were circular and rectangular huts made of timber and thatch, as the Aryans were still nomadic. Over time, the settlements grew and cities developed with rectangular plans divided into sectors. The concept of Vastupurusa, which determined the placement of buildings based on the imagined pinning of a demon to the ground, influenced traditional Hindu architecture.