Between 1492 and 1504, the Italian navigator and explorer Christopher Columbus[a] led four transatlantic maritime expeditions in the name of the Catholic Monarchs of Spain to the Caribbean and to Central and South America.

Many Europeans of Columbus's day assumed that a single, uninterrupted ocean surrounded Europe, Asia and Africa, although Norse explorers had colonized areas of North America beginning with Greenland c. 986.

Portugal was the main European power interested in pursuing trade routes overseas, with the neighboring kingdom of Castile—the predecessor to Spain—having been somewhat slower to begin exploring the Atlantic because of the land area it had to reconquer from the Moors during the Reconquista.

The fledgling Spanish Empire decided to fund Columbus's expedition in hopes of finding new trade routes and circumventing the lock Portugal had secured on Africa and the Indian Ocean with the 1481 papal bull Aeterni regis.

[11] In fact, the knowledge that the Earth is spherical was widespread, having been the general opinion of Ancient Greek science, and gaining support throughout the Middle Ages (for example, Bede mentions it in The Reckoning of Time).

[12] Where Columbus differed from the generally accepted view of his time was in his incorrect assumption of a significantly smaller diameter for the Earth, claiming that Asia could be easily reached by sailing west across the Atlantic.

[21] To effectively make the return voyage, Columbus would need to follow the curving trade winds northeastward to the middle latitudes of the North Atlantic, where he would be able to catch the "westerlies" that blow eastward to the coast of Western Europe.

By sailing directly due west from the Canary Islands during hurricane season, skirting the so-called horse latitudes of the mid-Atlantic, Columbus risked either being becalmed or running into a tropical cyclone, both of which, by chance, he avoided.

[26] In May 1489, Isabella sent Columbus another 10,000 maravedis, and the same year the Catholic Monarchs furnished him with a letter ordering all cities and towns under their domain to provide him food and lodging at no cost.

[29] Isabella was finally convinced by the king's clerk Luis de Santángel, who argued that Columbus would bring his ideas elsewhere, and offered to help arrange the funding.

[29] In the April 1492 "Capitulations of Santa Fe", Columbus was promised he would be given the title "Admiral of the Ocean Sea" and appointed viceroy and governor of the newly claimed and colonized for the Crown; he would also receive ten percent of all the revenues from the new lands in perpetuity if he was successful.

As described in the abstract of his journal made by Bartolomé de las Casas, on the outward bound voyage Columbus recorded two sets of distances: one was in measurements he normally used, the other in the Portuguese maritime leagues used by his crew.

Las Casas originally interpreted that he reported the shorter distances to his crew so they would not worry about sailing too far from Spain, but Oliver Dunn and James Kelley state that this was a misunderstanding.

[52][j] Columbus wrote of the natives he first encountered in his journal entry of 12 October 1492:Many of the men I have seen have scars on their bodies, and when I made signs to them to find out how this happened, they indicated that people from other nearby islands come to San Salvador to capture them; they defend themselves the best they can.

On the night of 17 February, the Niña laid anchor at Santa Maria Island, but the cable broke on sharp rocks, forcing Columbus to stay offshore until morning when a safer location was found nearby.

[34][83][t][u] The fleet continued to the Greater Antilles, first sighting the eastern coast of the island of Puerto Rico, known to its native Taino people as Borinquen, on the afternoon of 17 November 1493.

Upon landing, Columbus christened the island San Juan Bautista after Saint John the Baptist, preacher and prophet who baptized Jesus Christ, and remained anchored there for two days, 20 and 21 November 1493.

Fleet member Diego Álvarez Chanca recounts that as they sailed along the southern coast of Puerto Rico, a Taino woman and boy, who had volunteered to join them on-board in Guadeloupe, after having been rescued together with a group of at least 20 women the Caribs had been keeping as sex slaves, swam ashore, having recognized their homeland.

"[99] By 1494, Columbus had shared his viceroyship with one of his military officers named Margarit, ordering him to prioritize Christianizing the natives, but that part of their noses and ears should be cut off for stealing.

[102][better source needed] That month, Columbus shipped approximately 500 of these Americans to Spain to be sold as slaves; about 40% died en route,[59][101] and half of the rest were sick upon arrival.

According to the abstract of Columbus's journal made by Bartolomé de Las Casas, the objective of the third voyage was to verify the existence of a continent that King John II of Portugal suggested was located to the southwest of the Cape Verde Islands.

Three of the ships headed directly for Hispaniola with much-needed supplies, while Columbus took the other three in an exploration of what might lie to the south of the Caribbean islands he had already visited, including a hoped-for passage to continental Asia.

[121] An easterly wind finally propelled them westwards, which was maintained until 22 July, when birds flying from southwest to northeast were sighted, and the fleet turned north in the direction of Dominica.

[135] An entry in his journal from September 1498 reads: "From here one might send, in the name of the Holy Trinity, as many slaves as could be sold ..."[136] Columbus was eventually forced to make peace with the rebellious colonists on humiliating terms.

[138] As an added insult, in 1499, the Portuguese explorer Vasco da Gama returned from his first voyage to India, having sailed east around the southern tip of Africa—unlocking a sea route to Asia.

I beg your graces, with the zeal of faithful Christians in whom their Highnesses have confidence, to read all my papers, and to consider how I, who came from so far to serve these princes... now at the end of my days have been despoiled of my honor and my property without cause, wherein is neither justice nor mercy.

[156] On 14 March 1502, Columbus started his fourth voyage with 147 men and with strict orders from the king and queen not to stop at Hispaniola, but only to search for a westward passage to the Indian Ocean mainland.

"[158] Accompanied by his stepbrother Bartolomeo, Diego Mendez, and his 13-year-old son Ferdinand, he left Cádiz on 9 May 1502, with his flagship, Capitana, as well as the Gallega, Vizcaína, and Santiago de Palos.

Never did the sky look more terrible; for one whole day and night it blazed like a furnace, and the lightning broke with such violence that each time I wondered if it had carried off my spars and sails; the flashes came with such fury and frightfulness that we all thought that the ship would be blasted.

[183] On 25 September 1513, the Spanish conquistador Vasco Núñez de Balboa, exploring overland, became the first European to encounter the Pacific Ocean from the shores of the Americas, calling it the "South Sea".