Treaty of Tordesillas - Tordesillas Meridian

Tordesillas Meridian

The Treaty of Tordesillas only specified the line of demarcation in leagues from the Cape Verde Islands. It did not specify the line in degrees, nor did it identify the specific island or the specific length of its league. Instead, the treaty stated that these matters were to be settled by a joint voyage, which never occurred. The number of degrees can be determined via a ratio of marine leagues to degrees applied to the Earth regardless of its assumed size, or via a specific marine league applied to the true size of the Earth, called "our sphere" by Harrisse.

• The earliest Spanish opinion was provided by Jaime Ferrer in 1495 at the request of and to the Spanish king and queen. He stated that the demarcation line was 18° west of the most central island of the Cape Verde Islands, which is Fogo according to Harrisse, having a longitude of 24°25'W of Greenwich, hence Ferrer placed the line at 42°25'W on his sphere, which was 21.1% larger than our sphere. Ferrer also stated that his league contained 32 Olympic stades, or 6.15264 km according to Harrisse, thus Ferrer's line was 2,276.5 km west of Fogo at 47°37'W on our sphere.

• The earliest surviving Portuguese opinion is on the Cantino planisphere of 1502. Because its demarcation line was midway between Cape Saint Roque (northeast cape of South America) and the mouth of the Amazon River (its estuary is marked Todo este mar he de agua doçe (All of this sea is fresh water) and its river is marked Rio grande (great river)), Harrisse concluded that the line was at 42°30'W on our sphere. Harrisse believed the large estuary just west of the line on the Cantino map was that of the Rio Maranhão (this estuary is now the Baía de São Marcos and the river is now the Mearim), whose flow is so weak that its gulf does not contain fresh water.

• In 1518 another Spanish opinion was provided by Martin Fernandez de Enciso. Harrisse concluded that Enciso placed his line at 47°24'W on his sphere (7.7% smaller than ours), but at 45°38'W on our sphere using Enciso's numerical data. Enciso also described the coastal features near which the line passed in a very confused manner. Harrisse concluded from this description that Enciso's line could also be near the mouth of the Amazon between 49° and 50°W.

• In 1524 the Spanish pilots (ships' captains) Thomas Duran, Sebastian Cabot (son of John Cabot), and Juan Vespuccius (nephew of Amerigo Vespucci) gave their opinion to the Badajoz Junta, whose failure to resolve the dispute led to the Treaty of Saragossa. They specified that the line was 22° plus nearly 9 miles west of the center of Santo Antão (the westernmost Cape Verde island), which Harrisse concluded was 47°17'W on their sphere (3.1% smaller than ours) and 46°36'W on our sphere.

• In 1524 the Portuguese presented a globe to the Badajoz Junta on which the line was marked 21°30' west of Santo Antão (22°6'36" on our sphere).