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 is located in Thanjavur district, 15 km from Tiruchirapalli and 45 km from Tanjavur. It is the fourth oldest water-diversion or water-regulator structure 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.