To attract Muslim traders along the routes traveled in North Africa, the first factory trading post was built in 1445 on the island of Arguin, off the coast of Mauritania. Portuguese merchants accessed the interior via the Senegal and Gambia rivers, which bisected long-standing trans-Saharan routes. They brought in copperware, cloth, tools, wine, and horses, and later included arms and ammunition. In exchange, they received gold from the mines of Akan, Guinea pepper (a trade which lasted until Vasco da Gama reached India in 1498), and ivory. The expanding market opportunities in Europe and the Mediterranean resulted in increased trade across the Sahara. There was a very small market for African slaves as domestic workers in Europe, and as workers on the sugar plantations of the Mediterranean and later Madeira. The Portuguese found they could make considerable amounts of gold by transporting slaves from one trading post to another, along the Atlantic coast of Africa: Muslim merchants had a high demand for slaves, which were used as porters on the trans-Saharan routes, and for sale in the Islamic Empire.