Aden is an important port in the south of the country and until unification with the north in 1990 was capital of the Peoples Democratic Republic of Yemen. Its ancient, natural harbour lies in the crater of a long extinct volcano and the town has several sub-centres around the bay. Long coveted because of its position on the sea route from Europe to India, it was ceded to Britain in 1839 and the British East India Company stationed troops here to prevent attacks against shipping. It was ruled as part of British India until 1937 when it became a colony in its own right. After the loss of Suez in 1956 it was Britain’s main base in the area until independence was granted in 1967. The city has several interesting sights, best known among them are the cisterns of Tawila, huge tanks that although the date of construction is disputed are thought to have been able to contain 19 million gallons of water.