The Treaty of Tordesillas: Agreement and Implementation

The Treaty of Tordesillas emerged from competition between the two Iberian crowns over rights to overseas navigation and expansion. After Columbus returned to Europe in 1493, existing maritime arrangements between the Castilian Crown and Portugal were challenged. Papal bulls that year placed a dividing line one hundred leagues west of the Azores or Cape Verde islands. Portugal considered this to leave too little room for its routes and demanded that the line be moved farther west.

Negotiations in 1493 failed to resolve the disagreement. In March 1494, Ruy de Sousa, his son João de Sousa, and Aires de Almada negotiated with Ferdinand and Isabella on behalf of King João II of Portugal. The final text was agreed on June 7 at Tordesillas, near Valladolid. Castile was represented by the plenipotentiaries Enrique Enríquez, Gutierre de Cárdenas, and Rodrigo Maldonado.

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The treaty set out the representatives’ authority, authenticated in the presence of notaries and witnesses. Two identical documents were delivered to the parties, each carrying evidentiary force. It required the exchange within one hundred days of instruments of ratification bearing the monarchs’ own signatures and seals, and on the Castilian side also required the assent and signature of Prince Juan. Agreement by representatives, royal ratification, and exchange of documents were connected procedures.

Ferdinand, Isabella, and the prince ratified the treaty at Arévalo on July 2, 1494, and João II of Portugal ratified it at Setúbal on September 5. The treaty further required both sides to uphold the agreement, not seek papal release from their oath, and instead request papal confirmation of the agreed terms. These dates mark signature and the separate ratifications. They do not establish that the maritime boundary had been surveyed on the same day or that the overseas territories had already come under actual rule.

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The central provision prescribed a straight line from the North Pole to the South Pole, 370 leagues west of the Cape Verde islands. Islands and mainland territories already discovered or to be discovered east of the line fell within Portuguese claims, and those west of it within Castilian claims. Both parties undertook not to explore, trade, or conquer in the other’s sphere. Even land discovered by their own ships had to be delivered to the other crown if it lay within that crown’s allotted area.

Castilian ships traveling to the western sphere inevitably had to pass through Portuguese waters and therefore received safe passage. In principle, however, they had to follow a direct route, could deviate only because of adverse weather, and could not claim discoveries within the Portuguese sphere along the way. These were claims and obligations between two crowns, not an allocation of land jointly agreed with the inhabitants of the territories concerned.

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The treaty also addressed the possibility that ships already at sea would bring back news of discoveries. Lands found by the Castilian side before June 20, 1494, within the first 250 leagues west of Cape Verde would still belong to Portugal; those within the following band of 120 leagues could belong to Castile. Discoveries after the deadline reverted to the general rule. The boundary arrangement thus involved both geographical limits and a cutoff date, rather than a line alone.

To establish the line, each side originally planned to dispatch one or two caravels within ten months, meeting at Gran Canaria before proceeding to Cape Verde to measure westward. They were to send equal numbers of pilots, astronomical specialists, and sailors, with personnel traveling on the other side’s ships so they could observe jointly, agree, and sign the results. If the line crossed land, markers or towers were to be erected. These were intended procedures, not completed works.

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The original timetable was not fulfilled. On May 7, 1495, Ferdinand and Isabella signed a new agreement in Madrid stating that experts from both sides should first agree on a method of demarcation to avoid disputes after departure. It arranged a meeting of experts on the border in September and expressly postponed the fleet’s sailing. If an island or mainland suitable for demarcation was later discovered, one party would notify the other and the agreed method would then be applied.

The new document also required future nautical charts to show the dividing line so that navigators would know where they were permitted to go. Davenport’s documentary introduction notes, however, that the principal arrangements remained unfulfilled. A written commitment could specify personnel, deadlines, and documentation, but could not automatically remove disagreements over measurement conditions and political interests.

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Sánchez emphasizes that reliable methods for precise longitude determination were still lacking in 1494. Which Cape Verde island served as the starting point and how nautical leagues were represented on a chart also affected the line’s position. The Cantino planisphere of 1502 already depicted the division and marked Portuguese discoveries and flags along the Brazilian coast. Maps thus became instruments for displaying royal claims, but a line on a map did not mean that both sides had jointly recognized an accurately surveyed boundary.

The dispute later extended to the Spice Islands. At the Badajoz–Elvas conference of 1524, experts still debated whether to use charts or a globe, how to position the Cape Verde islands, and where to begin measuring distance. The treaty established a shared framework for prolonged negotiation while closely linking diplomacy, navigational knowledge, and colonial expansion. Its practical effects must be understood through subsequent maps, voyages, and negotiations.

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