From the voyages of the Portuguese navigators under the patronage of Henry the Navigator in the 15th century to the transcontinental expeditions of Henry Morton Stanley in the 1870s, European exploration of Africa gradually transformed European geographic knowledge of the continent. Early expeditions focused primarily on maritime navigation and access to the gold, spice, and Indian Ocean trade networks. Explorers such as Gil Eanes, Bartolomeu Dias, and Vasco da Gama established new Atlantic and Indian Ocean sea routes during the reigns of John I of Portugal (reign 1385–1433), John II of Portugal (reign 1481–1495), and Manuel I of Portugal (reign 1495–1521). During the 18th and 19th centuries, scientific curiosity, missionary activity, commercial ambition, and competition between European states drove explorers deeper into the Sahara, the Niger Basin, the Nile system, and the African Great Lakes. Expeditions by Mungo Park, Heinrich Barth, Richard Francis Burton, John Hanning Speke, and David Livingstone helped resolve long-standing European geographical questions concerning the Niger River, the source of the Nile, and the river systems of Central Africa.