engagement in long-distance trade: a small amount of imported pottery has been found, less than 1% of total pottery finds, mostly from the Gulf and dated to the 5th to 8th century. The similarity to contemporary sites such as Mkokotoni and Dar es Salaam indicate a unified group of communities that developed into the first centre of coastal maritime culture. The coastal towns appear to have been engaged in Indian Ocean and inland African trade at this early period. Trade rapidly increased in importance and quantity beginning in the mid-8th century and by the close of the 10th century Zanzibar was one of the central Swahili trading towns. Growth in Egyptian and Persian shipping from the Red Sea and the Persian Gulf revitalised Indian Ocean trade, particularly after the Fatimid Caliphate relocated to Fustat (Cairo). Swahili agriculturalists built increasingly dense settlements to tap into trade, these forming the earliest Swahili city-states. The Venda-Shona Kingdoms of Mapungubwe and Zimbabwe in South Africa and Zimbabwe, respectively, became a major producer of gold around this same period. Economic, social, and religious power was increasingly vested in Kilwa, Tanzania's major medieval city-state. Kilwa controlled a number of smaller ports stretching down to modern-day Mozambique. Sofala became the major gold emporium and Kilwa grew rich off the trade, lying at the southern end of the Indian Ocean Monsoons. Kilwa's major rivals lay to the north, in modern-day Kenya, namely Mombasa and Malindi. Kilwa remained the major power in East Africa until the arrival of the Portuguese at the end of the 15th century. Colonial Claiming the coastal strip, Omani Sultan Said bin Sultan moved his capital to Zanzibar City in 1840. During this time, Zanzibar became the centre for the east African slave trade. Between 65 and 90 per cent of the Arab-Swahili population of Zanzibar was enslaved. One of the most infamous slave traders on the East African coast was Tippu Tip, who was the grandson of an enslaved African. The Nyamwezi slave traders operated under the leadership of Msiri and Mirambo. According to Timothy Insoll, "Figures record the exporting of 718,000 slaves from the Swahili coast during the 19th century, and the retention of 769,000 on the coast." In the 1890s, slavery was abolished. In 1863, the Holy Ghost Mission established an early reception center and depot at Zanzibar. In 1877, responding to appeals of Henry Stanley following his trans-Africa expedition, and permission