Portuguese Empire years for the Portuguese to follow up on Dias's voyage to the Cape of Good Hope, though it has also been speculated that other voyages were in fact taking place in secret during this time. Whether or not this was the case, the long-standing Portuguese goal of finding a sea route to Asia was finally achieved in a ground-breaking voyage commanded by Vasco da Gama. The squadron of Vasco da Gama left Portugal in 1497, rounded the Cape and continued along the coast of East Africa, where a local pilot was brought on board who guided them across the Indian
Portuguese discoveries tip of Africa, disproving the view that had existed since Ptolemy that the Indian Ocean was separate from the Atlantic. Also at this time, Pêro da Covilhã reached India via Egypt and Yemen, and visited Madagascar. He recommended further exploration of the southern route. As the Portuguese explored the coastlines of Africa, they left behind a series of padrões, stone crosses inscribed with the Portuguese coat of arms marking their claims, and built forts and trading posts. From these bases, the Portuguese engaged profitably in the slave and gold trades. Portugal enjoyed a virtual monopoly of the Atlantic slave trade