Treaty of Badajoz (1267)

The Treaty of Badajoz was signed in Badajoz on 16 February 1267 between King Alfonso X of Castile and King Afonso III of Portugal, establishing mutual assistance and friendship between the parties. The accord would see Alfonso X renounce all rights to the Kingdom of the Algarve, including a personal agreement with Denis of Portugal to support Alfonso with fifty knights. Following the treaty, Alfonso X continued to use the title king of the Algarve although it was probably used in reference to the territory of Niebla. The treaty also reinforced Portugal's sovereignty, by confirming the end of vassalage relations between Portuguese kings and the monarchs of León. Lastly, the border between the two kingdoms was agreed as the course of the Guadiana river, between its mouth and the river Caia. This led to the concession of some conquered territory by Portugal to Castile to the east of the river.

The Treaty of Badajoz was a foundation in setting the borders between the two kingdoms and paramount for the signing of the Treaty of Alcañices in 1297. This would settle the Portuguese border with Castile until 1801, when another Treaty of Badajoz was signed, when Portugal ceded a number of territories, including the town of Olivença this last concession being voided by the 1807 Treaty of Fontainebleau breaching the clauses of the previous treaty.