Grand Anicut

Kallanai (also known as the Grand Anicut) is an ancient dam built by Karikala of Chola dynasty in 150 CE. It is built (in running water) across the Kaveri river flowing from Tiruchirapalli District to Thanjavur district, Tamil Nadu, India. The dam located in Thanjavur district. Located at a distance of 15 km from Tiruchirapalli, 45 km from Tanjavur. 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. From Wikipedia