In July 1539, Cortés sent Francisco de Ulloa to sail the Gulf of California with three small vessels. He made it to the mouth of the Colorado River, then sailed around the peninsula as far as Cedros Island. This proved that Baja California is a peninsula. The next year, an expedition under Hernando de Alarcón ascended the lower Colorado River to confirm Ulloa's finding. Alarcón may thus have become the first to reach Alta California. European maps published subsequently during the 16th century, including those by Gerardus Mercator and Abraham Ortelius, correctly depict Baja California as a peninsula, although some as late as the 18th century do not. The account of Ulloa's voyage marks the first-recorded application of the name "California". It can be traced to the fifth volume of a chivalric romance, Amadis de Gallia, arranged by Garci Rodríguez de Montalvo and first printed around 1510, in which a character travels through an island called "California".