Several geographic and economic factors encouraged early European exploration, including the Turkish blockade of Mediterranean trade routes to Asia and high prices charged by Arab middlemen. Portugal led exploration efforts to find alternate routes, establishing trading posts in Africa and Brazil. Technological advances in shipbuilding and navigation, such as the astrolabe and improved maps, also enabled longer voyages. Prince Henry of Portugal established a navigation school and sponsored voyages down the African coast. Spain subsequently sponsored voyages that led to European discovery and colonization of the Americas.