During the Early Middle Ages

, sailboats in the Mediterranean continued to use a triangular screen developed during the Roman Empire. Over time, shipbuilders experimented with more than one pole. In the 1000s AD, Italian merchants from Venice, Genoa, and Pisa used ships with three poles, each with a triangular or lateen screen. Using three screens, the sailors more easily adjust the ship in a change of direction.

However, the Mediterranean seafarers of the Middle Ages still had unresolved issues. They want to sail south along the African Atlantic coast, to trade with West Africa using a capala instead of crossing the Sahara. It would be cheaper to bring African gold with a ship than with a camel. They can indeed sail to West Africa but can not sail back because the wind along the coast almost always blows south rather than north. In addition, medieval sailors were unable to sail further south due to the flow of water flowing north along the coast. To sail there, they must move the screen back and forth in order to sail against the wind. Portuguese shipbuilders eventually found a way of combining rectangular and lateen screens to sail downwind.

After the Portuguese shipbuilders managed to find a way of navigating the coast of Africa, they became interested in sailing across the Atlantic Saumdra, wanting to find their way to China. The Portuguese sailors have just gained the Chinese invention, the compass. Compass, coupled with astrolabes, makes it possible to know the direction of travel in the oceans even though it is away from the mainland.

But to get ready to cross the Atlantic, shipbuilders are also redesigning their screens. Vasco da Gama and Columbus use three poles, two poles with rectangular screens, and a back pole with lateen screens.