The island of Guam was first discovered by Europeans when Portuguese explorer Ferdinand Magellan, sailing for Spain, arrived there on March 6, 1521. Magellan's expedition marked the first known European contact with Guam, and he named the island group "Islas de los Ladrones" (Islands of Thieves) due to the interactions with the local Chamorro people at that time. Although Magellan's visit was the first European discovery of Guam, the island was not officially claimed by Spain until 1565 by Miguel López de Legazpi. Spanish colonization began later, in 1668, with the arrival of Jesuit missionaries.