The first European to reach the Cape of Good Hope, thereby presumably discovering it, was Bartolomeu Dias in 1488. Prior to that time, when it was considered unwise to question ancient authority, it was commonly believed that the southern tip of Africa was joined to the northern coast of Eurasia, which meant that a water route around Africa to Asia was impossible. This was based on the writings of Aristotle and Claudius Ptolemy. Dias sailed under the authority of King John II of Portugal in hopes of finding if there was in fact a water route, and also to locate a mysterious priest-king known to Europeans as Priester John. Dias actually rounded the Cape thus demonstrating that it was possible to sail around Africa, but did not complete his voyage as his crew refused to travel further. Later, in 1498, Vasco da Gama completed the entire journey and landed at Calcutta, India.