To ensure their monopoly on trade, Europeans (beginning with the Portuguese) attempted to install a mediterranean system of trade which used military might and intimidation to divert trade through ports they controlled; there it could be taxed. In 1415, Ceuta was conquered by the Portuguese aiming to control navigation of the African coast. Young prince Henry the Navigator was there and became aware of profit possibilities in the Trans-Saharan trade routes. For centuries slave and gold trade routes linking West Africa with the Mediterranean passed over the Western Sahara Desert, controlled by the Moors of North Africa.