Kallanai (also known as the Grand Anicut) is an ancient dam. It is built (in running water) across the Kaveri river flowing from Tiruchirapalli District to Thanjavur district,Tamilnadu, India. The dam located in Thanjavur district. Located at a distance of 15 km from Tiruchirapalli, 45 km from Tanjavur, the dam was originally constructed during the reign of Chola king Karikalan in c. 100 BC – c. 100 AD. It is the fourth oldest water diversion or water-regulator structures in the world and the oldest in India that is still in use. Because of its spectacular architecture, it is one of the prime tourist spots in Tamil Nadu.
