Coastal traders settled in Unyamwezi, some with hundreds of well-armed retainers. The Nyamwezi provided most of the porters for the caravans organized by the coastal Arabs and Swahilis,  and also conducted their own caravans. The Nyamwezi were long-distance traders throughout East Africa. Ivory was not widely used by the Nyamwezi, but at some point they became aware that there was an overseas market for the product, and began to carry ivory along the route from Tabora down to the Indian Ocean coast opposite Zanzibar. There are records of Sultan Sayyid Said of Zanzibar negotiating with envoys from Unyamwezi in 1839 for safe passage for caravans to the interior. The Nyamwezi did not sell their own people as slaves, since they needed manpower for the ivory trade, but after the 1850s the slave trade began to become important. Slaves brought from the Congo Basin or the Great Lakes region would be held at Tabora, then sent down to the coast in small groups for onward shipment. Early in 1844 Sultan Sayyid Said gave the German missionary Johann Ludwig Krapf (1810–1881) permission to establish a mission on the coast. Krapf arrived in Mombasa on 13 March 1844. He was joined in 1846 by Johannes Rebmann (1820–1876). On 12 November 1848 Rebmann started a journey into the interior. The "Church Missionary Intelligencer" reported that, "The ultimate object, which our Missionaries had in view, has been to reach Uniamési, that interior country where the roads to East Africa and West Africa diverge." Uniamési was said to lie about 150 to 200 hours to the west of the Chagga kingdom, which lay on the slopes of Mount Kilimanjaro. On 10 June 1849 Jakob Erhardt (1823–1901) and John Wagner arrived at the Rabbai Mpia mission station near Mombasa. Wagner died on 1 August 1849. In the spring of 1850 Erhardt and Krapf traveled by dhow down the East African coast from Mombasa. On the journey they met traders from Unyamwezi. Krapf recorded that caravans of three to four thousand men from Unyamwezi would arrive at the coast in December after a three-month journey, and would leave on the return journey in March or April.