The sixteenth century in the Pacific belonged to the Spanish. In 1520 Ferdinand Magellan, a Portuguese, sailing under the Spanish flag, found the strait at the southern end of South America that bears his name, and on leaving it sailed into the South Sea. The Pacific received its misleading name from the unusually calm weather Magellan experienced while crossing it. Sailing into this unknown sea, Magellan established for the first time the fact that it was a great ocean. By bad luck, Magellan managed to cross the Pacific without sighting any fertile islands before reaching the Marianas. Although these islands may seem numerous on a modern chart, they are actually few and far between. The expedition suffered from an acute shortage of fresh water and food that could have been relieved if inhabited islands had been found. The only islands sighted were low, waterless islands, probably some of the northern Marshalls, which Magellan named St. Paul and Shark Islands, and, because of their unfortunate nature, grouped them together as the Desaventuradas.
These islands presented for the first time a major problem that was to plague the cartographers of the Pacific until the time of Captain Cook. Although the navigational instruments of this period permitted the navigators to fix latitude with some degree of accuracy, they were unable to fix their longitude except by dead reckoning. Serious errors were made in estimating the actual distance traveled until the circulation of both the winds and the currents was understood. It was not until 1736 that John Harrison invented an accurate chronometer that permitted navigators to fix longitude accurately, and even then it was not used in the Pacific until the second voyage of Captain Cook in 1773.
One of Magellan's pilots misestimated the width of the Pacific by about 3000 nautical miles. His successors continued to guess the position of land that they discovered or rediscovered. In time the Pacific charts were filled with islands that were incorrectly charted.
On March 6, 1521, the starving sailors sighted fertile islands. Magellan named these the Islands of the Lateen Sails, but they were renamed the Ladrones or Isles of Thieves because of the misunderstanding between the natives and the Europeans over property. Eventually they were named the Marianas after the wife of Philip IV, Queen Maria Anna, who financed missions there. Magellan sailed westward to the Philippines, which eventually received their name in honor of Philip II. Magellan became embroiled in a local quarrel and was killed on a small island near Cebu. Sebastian del Cano, the second in command, took the surviving ship, the Victoria, back to Spain, completing the first circumnavigation of the globe. While authorities differ as to the exact numbers, it appears that only 18 of the approximately 268 men who originally sailed from Spain returned on the Victoria. This attrition, of course, was to be typical of long Pacific voyages until Captain Cook overcame scurvy.
There was considerable question in Europe, in view of the problems concerning longitude and the actual size of the earth, as to whether these islands as well as the Moluccas fell on the Portuguese or the Spanish side of the Papal Line of Demarkation as modified by the Treaty of Tordesillas of 1494. The Spanish sold their claim to the Moluccas but retained the Philippines.