All three assemblies - Sabha, Samiti, and Vidatha - are mentioned in the Rigveda. The Sabha was likely an assembly of elders or elite, involved in deliberation and judicial matters. The Samiti was probably a more general assembly of the people or the tribe, dealing with political affairs, including electing the king. The Vidatha appears to be the oldest assembly, with diverse functions including religious ceremonies, military activities, and distribution of wealth.