Sea in culture of barbarian invaders and knowledge of geography took a backward step. In the seventh century, Isidore of Seville produced a "wheel map" in which Asia, Africa and Europe were arranged like segments in an orange, separated by the "Mare Mediterranean", "Nilus" and "Tanais" and surrounded by "Oceanus". It was not until the fifteenth century that Ptolemy's maps were used again and Henry the Navigator of Portugal initiated ocean exploration and maritime research. Encouraged by him, Portuguese navigators explored, mapped and charted the west coast of Africa and the Eastern Atlantic and this knowledge prepared the way for the great voyages
Western imperialism in Asia victory enabled Portugal to implement its strategy of controlling the Indian Ocean. Early in the 16th century Afonso de Albuquerque (left) emerged as the Portuguese colonial viceroy most instrumental in consolidating Portugal's holdings in Africa and in Asia. He understood that Portugal could wrest commercial supremacy from the Arabs only by force, and therefore devised a plan to establish forts at strategic sites which would dominate the trade routes and also protect Portuguese interests on land. In 1510, he conquered Goa in India, which enabled him to gradually consolidate control of most of the commercial traffic between Europe and Asia,