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
East Africa main goal on the Swahili coast was to take control of the spice trade from the Arabs. At this stage, the Portuguese presence in East Africa served the purposes of controlling trade within the Indian Ocean and securing the sea routes linking Europe to Asia. Portuguese naval vessels were very disruptive to the commerce of Portugal's enemies within the western Indian Ocean and were able to demand high tariffs on items transported through the sea due to their strategic control of ports and shipping lanes. The construction of Fort Jesus in Mombasa in 1593 was meant to solidify Portuguese hegemony