The “global economy” of the Middle Ages was created by linking the Indian Ocean trading networks with those of the Mediterranean Sea and its African and European hinterlands. By the eighth century, Spain and the African shores of the Mediterranean were part of the expanding empire that Muslims called dar al-islam (“the house of Islam”) and had commercial links, both maritime and overland, with Egypt and Syria. Between the years 800 and 1000, the Mediterranean was dominated by Muslim shipping.
The Fatimid Dynasty arose in what is now Tunisia in the early 10th century. Their subsequent invasion of Egypt gave them control of the most important port of the eastern Mediterranean: Alexandria. This famous port linked the new Fatimid capital of Cairo, founded in 969, to the whole Mediterranean world via the Nile. With the conquest of Egypt, the Fatimids made a concerted drive to shift the economic center of the Islamic world from Baghdad, capital of their political rivals, the Abbasids, to Cairo. They revived the Red Sea as the principal conduit of maritime trade with the Indian Ocean, restoring that route to the role it had played in Ptolemaic and Roman times.
via Saudi Aramco World : Monsoons, Mude and Gold.