<Tr> <Th> Length </Th> <Td> 0.329 km (1,079 ft) </Td> </Tr> <Tr> <Th> Width (base) </Th> <Td> 20 m (66 ft) </Td> </Tr> <P> Kallanai (also known as the Grand Anicut, Tamil: கல்லணை) is an ancient dam, which is built (in running water) across the Kaveri river in Thanjavur District in the state of Tamil Nadu in India . Located at a distance of 15 km from Tiruchirappalli, the dam was originally constructed by the Chola king Karikalan in 2nd century AD . It is located on Kaveri river approximately 20 KM from Trichy city, the dam falls under Thanjavur district . and is the fourth - oldest water - diversion or water - regulator structures in the world and the oldest in India which is still in use . </P> <P> The dam was originally built by King Karikalan of the Chola Dynasty in the 2nd century AD . The dam is located on the River Kaveri, approximately 20km from the city of Tiruchirapalli. The idea behind the construction of the dam was to divert the river to the delta districts thereby boosting irrigation . The dam was re-modeled by the British during the 19th century . In 1804, Captain Caldwell, a military engineer, was appointed by the British to make a study on the Kaveri river and promote irrigation for the delta region . He found that a large amount of water passed onto the Kollidam leaving behind a small volume for irrigation purposes . Caldwell initially proposed a solution by raising the dam and hence raised the dam stones to a height of 69 centimetres (27 in), thus increasing the capacity of the dam . Following this, Major Sim proposed the idea of undersluices across the river with outlets leading to the Kollidam River (Coleroon) thus preventing formation of silt . The Lower Anaicut built by Sir Arthur Cotton in 19th century CE across Coleroon, the major tributary of Cauvery, is said to be a replicated structure of Kallanai . </P>

When was the first dam built in india