Ferdinand Magellan reached the Mariana Islands and Guam

Heading northwest, the crew reached the equator on February 13, 1521.

On 6 March they reached the Marianas and Guam. Magellan called Guam the "Island of Sails" because they saw a lot of sailboats. They renamed it to "Ladrones Island" (Island of Thieves) because many of Trinidad's small boats were stolen there.

The Marianas were sighted in 1521 by Ferdinand Magellan, a Portuguese explorer sailing for Spain. The islands, known as the Ladrones Islands (Thieves Islands), were not colonized until 1668, when Spanish Jesuit settlers arrived and claimed them for Spain. They renamed the islands for Mariana of Austria, then regent of Spain. In 1898, Guam was ceded by Spain to the United States, and the following year Germany purchased the rest of the island group.

The first known contact between Guam and the West occurred when Ferdinand Magellan anchored his small 3-ship fleet in Umatac Bay on March 6, 1521. Hungry and weakened from their long voyage, the crew hastily prepared to go ashore and restore provisions. However, the excited native Chamorro's, who did not share the Spaniards concept of ownership, canoed out first and began helping themselves to everything that was not nailed down. The weakened sailors had trouble fending off the tall and robust natives until a few shots from the Trinidad's big guns frightened them off the ship and they retreated into the surrounding jungle. Magellan was eventually able to obtain rations and offered iron, a commodity highly prized by Neolithic peoples, in exchange for fresh fruits, vegetables and water. Details of Magellan's visit, and the first known Western documentation of Guam and the Chamorro, come from the journal of Antonio Pigafetta, Magellan's chronicler and one of only 18 original crew members to survive Ferdinand Magellan's ill-fated circumnavigation of the globe.

Convinced the Spice Islands were only a short sail away, Magellan led his ships across the Pacific, discovering the Marianas Islands and Guam. Although Magellan named them the Islas de las Velas Latinas (Islands of the Triangular Sails) the name Islas de los Ladrones (Islands of Thieves) stuck, because locals made off with one of the landing boats after giving Magellan’s men some supplies. Pressing on, they landed on Homonhon Island in the present-day Philippines. Magellan found he could communicate with the people, as one of his men spoke Malay. He had reached the Eastern edge of the world known to Europeans.