Archaeological research on the Swahili is linked to navigation and trade in the Indian Ocean. Mogadishu, in Somalia, formed the northern boundary of the Swahili cultural area. The stretch of coast between this city and the Lamu archipelago is nicknamed the benadir, an Arabic-Persian word meaning “the coast of ports”. The southern boundary of Swahili culture is the Bay of Sofala in today’s Mozambique. It is within this area that Muslim traders came to search for gold. In the medieval era, Arab geographers divided the African coast into four regions: sailors first reached the land of the barbarians or Bilâd al-Barbar; next they arrived at the land of Zanj or Bilâd al-Zanj, situated between the Somali river Shebele and the island of Zanzibar; then they arrived at the land of Sofala, Bilâd al-Sufâla, a zone between the mouths of the Zambezi and Limpopo rivers, also called Sofala the Golden or Sufâla al-dhahab; and finally a number of sailors went all the way to the mysterious land of Wâk-wâk, the large island of Madagascar. Long-distance trade is thus at the center of Swahili culture. Coastal cities formed an interface between the African highlands and the merchants of the Indian Ocean.
East Africa exported mostly raw materials; these commercial products are mostly invisible to archaeologists, comprising organic materials such as ivory, skins, cloth or wood. One of the most prized products was ivory. Tusks were generally sold raw throughout the cities of Vumba, Mombasa, Malindi, Lamu and Pate. The polishing of ivory occurred in the importing countries, for example in Fatimid Cairo. In addition to income earned from trade and fishing, Swahili urban elites owned plantations enabling them to meet their needs. Populations from the coastal hinterland provided other agricultural products, from hunting or gathering. Various Swahili agricultural products were exported, such as coconut and rice. Archives from the customs of Aden, dating from the fifteenth century, mention imported rice from Kilwa, but Neville Chittick argued that rice was only transited via Kilwa and actually came from Madagascar. Cloves were introduced in Zanzibar in 1818 by Sultan Sa‘îd and became the principal export of Pemba and Zanzibar. Mangrove timber was exported in large quantities to countries in the Persian Gulf, under the Arabic name of saj or mwangati in Kiswahili. The Swahilis also traded woodwork, such as doors or sculptured pediments, to Oman and Kuwait.
Al-Idrîsî speaks of several large iron-mining centers located between Malindi and Mombasa. Iron might have been the primary source of income for this region and India may have imported large quantities of the metal to make steel weapons (Freeman-Grenville 1962: 19-20). The author’s research in Gedi confirmed that iron production was very important in levels dating from the twelfth to thirteenth century. According to Muktahar ibn Tâhir al-Maqdisî, the Zanj country provided the Arabs with a lot of gold in the tenth century. The profits from trade played a significant role in the prosperity of the kingdom of Great Zimbabwe which operated many mines. The mined gold was sent to Sofala, a vassal locality in Kilwa Kisiwani from the twelfth century. The gold was redistributed by Kilwa, which thus held a monopoly until the fifteenth century. In 1501, Cabral boarded and searched two boats in Kilwa filled with gold (Freeman-Grenville 1962: 59-60). The “yellow metal” became the main African product of interest to the Portugese who later settled in Mozambique in the hinterland of Sofala (Horton 1996: 383). African gold, but also rock crystal, were raw materials that were in high demand under the Fatimids. Elements of rock crystal were found at several sites on the Swahili coast, in Gomani on the island of Tumbatu, in Gedi, Manda and Shanga. This mineral is foreign to coastal areas and came from the Kerio Valley and the Rift Valley.
The trade in humans was another aspect prized in Arab countries. Before the fifteenth century, most slaves came from Kenya and from the Horn of Africa, where the ports of Zeyla and Berbera were reputed for this merchandise. Few Portuguese texts concern the sale and export of slaves between the sixteenth and seventeenth century. Yet Ibn Battûta recounts that the holy war against Kilwa infidels was undertaken primarily to find slaves, more likely to represent trading on a commercial than a domestic level. The quantity of slaves exported to the Persian Gulf must have been considerable because a reported 500,000 outraged Zanj attacked al-Basra in 869 and retreated to al-Mukhtâra in lower Iraq, where they were defeated in 883. The quest for slaves had begun under the Sassanids in the fifth century and became industrial in scale in the nineteenth century under the Sultanate of Zanzibar. Slave traders collected slaves in the ports of Masselage in western Madagascar, in the archipelago of Kerimba in Mozambique, Kilwa Kisiwani or in Zanzibar. The dhows then returned through Pate all the way to Jeddah and Mocha in the Red Sea. Some slaves were shipped back to Turkey, Muscat, Sur and to the Sindh. The French islands of Bourbon and Mascarene (Mauritius and Réunion) exchanged many slaves for firearms especially between 1775-1804. Following the British ban on this trade, the Omani slave ships took refuge under the French flag from 1873 to 1891.
Swahili communities imported a lot of goods from the Persian Gulf. In the middle of the ninth century, the port of Siraf became a major trading center with East Africa. Al-Masûdî notes that vessels from Siraf left for Sofala and Waq-Waq (Madagascar). From the thirteen to the fifteen century, Africa was connected to other centers, in Yemen with Aden and in India with the Gujarat and the Deccan. This trade continued after the Portuguese intrusion. Finally during the nineteen century, trade was largely controlled by Oman. The Swahili imported a lot of manufactured products, including Islamic and Chinese ceramics, glass, metalwork and even carved stones for their mosques and cemeteries (Pradines 2010: 221-237). The study of these imports, in particular the ceramics, allows us to draw a new history of the Swahili coast and its contacts with other cultures of the Indian Ocean world.