Sion Causeway (also known as Duncan Causeway) is a major causeway in Bombay, India which connects Sion in Bombay with Kurla in Salsette. The construction of the causeway began in 1798 and was completed in 1805 by Jonathan Duncan, Governor of Bombay (1795–1811), at a cost of £5,037 (Rs. 50,370). In 1826, its breadth was doubled and improved at a further outlay of £4,000 (Rs. 40,000)[1][2] A volcanic tract extends from Carnac Bunder to Sion Causeway, and forms the entire of the chain of hills bordering the north-eastenn end of the island from the Sewri Fort to Sion.[3]