In the late pre-colonial period (late 19th century), it was the metropolis of a plantation society, which became dependent on slave labour (sources contradict whether the city was ever an important place for exporting slaves) but ivory caravans remained a major source of economic prosperity. Mombasa became the major port city of pre-colonial Kenya in the Middle Ages and was used to trade with other African port cities, the Persian Empire, the Arabian Peninsula, India and China. 16th-century Portuguese voyager Duarte Barbosa claimed, " is a place of great traffic and has a good harbour in which there are always moored small craft of many kinds and also great ships, both of which are bound from Sofala and others which come from Cambay and Melinde and others which sail to the island of Zanzibar."