Treaty of Tordesillas

Lore & Background

The Treaty of Tordesillas was intended to solve the dispute that arose following the return in 1493 of Christopher Columbus and his crew, who had sailed under the Crown of Castile, from their first voyage. On his way back to Spain, he first stopped at Lisbon, where he requested another meeting with King John II to prove to him that there were more islands to the southwest of the Canary Islands. After learning of the Castilian-sponsored voyage, the Portuguese king sent a threatening letter to the Catholic Monarchs, King Ferdinand and Queen Isabella, stating that by the Treaty of Alcáçovas signed in 1479 and by the 1481 papal bull Aeterni regis—which granted Portugal all lands south of the Canary Islands—the new discoveries fell within Portugal's sphere. The Portuguese king also stated that he was already making arrangements for a fleet (an armada led by Francisco de Almeida) to depart shortly and take possession of the new lands.

The Spanish rulers replied that Spain owned the islands discovered by Columbus and warned King John II not to permit anyone from Portugal to go there. Finally, the rulers invited Portugal to send ambassadors to begin diplomatic negotiations aimed at settling the rights of each nation in the Atlantic. On 4 May 1493, Pope Alexander VI decreed in the bull Inter caetera that all lands west of a pole-to-pole line 100 leagues west of any of the islands of the Azores or the Cape Verde Islands should belong to Castile, although territory under Christian rule as of Christmas 1492 would remain untouched. The bull did not mention Portugal or its lands, so Portugal could not claim newly discovered lands even if they were east of the line.

Another bull, Dudum siquidem, dated 1493, gave all mainlands and islands, 'at one time or even still belonging to India' to Spain, even if east of the line. The Portuguese King John II was not pleased with that arrangement, feeling that it gave him far too little land—it prevented him from possessing India, his near-term goal. By 1493, Portuguese explorers had reached the southern tip of Africa, the Cape of Good Hope. The Portuguese were unlikely to go to war over the islands encountered by Columbus.

Reader's Guide

The Treaty of Tordesillas only specified the line of demarcation in leagues from the Cape Verde Islands. It did not specify the length of the league, its equivalent in equatorial degrees, or which of the Cape Verde islands was intended. Instead, the treaty provided that these matters were to be settled by a joint voyage.

This voyage never occurred, and instead there were only a series of nonbinding expert opinions produced over the next several decades. Their computations were further complicated by remaining uncertainty about the exact equatorial circumference of the earth. As such, each proposed line can be variously computed using geographical leagues defined in terms of a degree using a ratio which applies regardless of the size of the earth or using a specifically measured league applied to the actual equatorial circumference of the earth, with allowances necessary for the imperfect Portuguese and Spanish knowledge of its true dimensions. The earliest Aragonese opinion was provided by Jaime Ferrer in 1495 at the request of Ferdinand and Isabella.

He stated to them that the demarcation line was 18° west of the most central island of the Cape Verde Islands, equivalent to 24°25 west of Greenwich. (Harrisse concludes Ferrer must have meant Fogo as this central island.) Thus, Ferrer placed the line at 42°25 W. on his sphere, which was 21.1% larger than the actual size of the earth. Harrisse further concludes from Ferrer's claim that his league contained 32 Olympic stades, that his line if perfectly measured would have an unspecified result.

Did You Know?

• The line was not strictly enforced—the Spanish did not resist the Portuguese expansion of Brazil across the meridian.
• The treaty was superseded by the 1750 Treaty of Madrid.