From Wikipedia: http://en.wikipedia.org/wiki/Stone_Town

Stone Town also known as Mji Mkongwe (Swahili for "old town") is the old part of Zanzibar City, the main city of Zanzibar, in Tanzania, as opposed to Ng'ambo (Swahili for 'the other side'). It is located on the western coast of Unguja, the main island of the Zanzibar Archipelago. Former capital of the Zanzibar Sultanate, and flourishing centre of the spice trade as well as the slave trade in the 19th century, it retained its importance as the main city of Zanzibar during the period of the British protectorate. When Tanganyika and Zanzibar joined each other to form the United Republic of Tanzania, Zanzibar kept a semi-autonomous status, with Stone Town as its local government seat.