The Portuguese journeys of discovery were but one element of the process of global exploration and expansion initiated with a fresh momentum in 15th-century Europe. This article attempts to outline the theoretical foundations and the range of knowledge about Africa that allowed the Portuguese to undertake the successful circumnavigation of that continent in 1488. The late 15th-century expeditions like that of Bartolomeu Dias had been preceded by centuries of accumulation of all kinds of information about the far-off regions that always excited the curiosity of the Europeans. Although it took a long time for the European scholarship to emerge from the Dark Ages, signs of a revival of geographical studies began to multiply in the 11th-12th centuries. Yet the new developments did little to extend the geographical horizon of the Europeans. Until the 15th century they still believed that the world was made up of the balanced landmasses of Europe, Asia and Africa (ie. North Africa). And, fantastic tales and strange inventions continued to be the stuff of virtually all of their knowledge of the world outside Europe. One of the major impulses of the breakthrough of the 14th-15th century was the arrival in Italy of Greek scholars from Constantinople. Frightened by the seemingly unstoppable march of the Turks, they escaped westwards taking with them their most precious possessions, books by classical authors hitherto unknown in the Latin Western Europe.