Born in 1450, Bartolomeu Dias (ca. 1450-1500) was the first Portuguese mariner to circumnavigate Africa. The voyage that made him famous in 1487 followed various attempts to investigate a passage to the Indies south of the African continent. The first expeditions were sponsored by Henry the Navigator (1394-1460) between 1450 and 1460, when the Turkish blockade of the Mediterranean prevented the use of traditional trade routes. Other navigators had reached the equator but had not ventured beyond because they lacked reliable astronomical measurements. Bartolomeu Dias sailed farther, rounding the Cape of Good Hope in May 1488. Besides the search for the route to the Indies, his expedition was motivated by the quest for Prester John, a Christian patriarch who was believed to rule a vast kingdom. Before his shipwreck and death on his third voyage in 1500, Dias made a second journey with Vasco da Gama (1469-1524), accompanying him to the Cape of Good Hope, then leaving him to sail on alone to the East Indies. Vasco da Gama left Lisbon on July 8, 1497, and followed a route never used before. Instead of sailing by sight along the African coast, he moved out to the Atlantic to take advantage of stronger winds, but did not round the Cape of Good Hope until November. On Christmas Day, he made landfall on the south-east coast of Africa. He called the spot Natal—the Portuguese word for Christmas—a name still in use today. In the following spring, he reached Mombasa, then Malindi, where he found an expert Yemenite navigator who accompanied him to India. On May 20, 1498, the first Portuguese ship entered the port of Calicut, on the Malabar coast, the hub of the spice and silk trade. After signing a trade treaty with the local ruler, Da Gama returned to Lisbon on September 9, 1499, having secured the monopoly of the spice trade between the East Indies and Europe for Portugal.