Treaty of Tordesillas

5 September 1494, at Setúbal

At Setúbal on 5 September 1494, King John II of Portugal formally ratified the agreement negotiated at Tordesillas. Spain's Ministry of Culture identifies the surviving document as the Portuguese confirmation and records the same date and place.

Ferdinand, Isabella and Prince Juan — whose signature the treaty expressly required — had already ratified at Arévalo on 2 July, so John's act completed the monarchs' approvals. The treaty had allowed 100 days from 7 June.

What the two crowns had agreed

Islands and mainlands east of a pole-to-pole line 370 leagues west of the Cape Verde islands went to Portugal; those west of it went to the rulers of Castile and their successors.

Both sides bound themselves not to send voyages for discovery, trade or conquest into the other's sphere, and to surrender discoveries made on the wrong side.

The treaty also planned a joint technical expedition — two or four caravels meeting at Grand Canary within ten months — to locate the line.

A line nobody could find

The text expressed no longitude at all, did not specify which Cape Verde island supplied the starting point, and contemporary navigators could not determine longitude reliably. The familiar 42°30′ W is a later reconstruction, and published reconstructions range roughly from 42° to 50° W.

The planned definitive survey was never achieved.

The two originals ended up across the border from each other: the Portuguese-language original is in Seville, the Castilian-language original in Lisbon.