The first known navigators were the Phoenicians, who 3000 years ago sailed the Mediterranean and beyond from their base near modern Lebanon. Justinian's mission to China in the 6th century A.D., the Viking expeditions of the 9th - 10th centuries, and Marco Polo's trip to China in 1270 opened new horizons. Then Portugal's Prince Henry the Navigator established a school of navigation whose influence touched a young Italian sailor and changed the world. Christopher Columbus sailed west in 1492, a date that began the Age of Exploration. Vasco da Gama in 1497 rounded Africa and sailed to India, opening the route to the east. Expeditions to the Americas by Amerigo Vespucci, Ferdinand Magellan, Cortes, Pizarro, Sir Walter Raleigh, and others soon followed. Over the 16th to 19th centuries came the inland explorations that created the modern world. Expanding settlement and commerce required better maps and navigation methods; a grid system of latitudes and longitudes, originally proposed by the ancient Greeks, was revived. Cartographers struggled with the task of representing a spherical earth on a flat map; dozens of map projections were developed. By the 20th century, new areas of discovery produced better navigational technology, more and more maps, and yet more horizons for future discovery.