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Portugal–Spain border

International border

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History

The Treaty of Limits between Portugal and Spain was signed in Lisbon in 1864 and ratified in Madrid in 1866, leaving unsettled a southern stretch because of the Olivenza and the Moura strifes. A 1926 Convention of Limits ratified the southern end of the border, incorporating a 1893 agreement concerning Moura, while the lands of Olivenza were left without demarcation because of Portuguese reluctance to recognise Spanish sovereignty over the territory.

A number of treaties have been signed between Portugal and Spain to define the boundaries between the two countries:

  • Treaty of Badajoz (1267) - Signed by king Alfonso X of Castile and King Afonso III of Portugal, establishing the Guadiana as roughly the southern border.
  • Treaty of Alcañices (1297) - Signed by King Denis of Portugal (grandson of king Alfonso X of Castile) and King Ferdinand IV of Castile, Olivença is ceded to Portugal.
  • Treaty of Badajoz (1801) - Olivença is ceded to Spain.
  • Congress of Vienna (1815) - Spain promises to return Olivença to Portugal, leaving this area of the border disputed ever since.
  • Treaty of Lisbon (1864) - This abolished the Couto Misto microstate, partitioning it between Spain and Portugal, while leaving the Olivenza sector unmapped due to the unresolved sovereignty dispute (see The undefined sector).
  • Convention of Limits (1926) - Demarcating the border from the confluence of Ribeira de Cuncos with the Guadiana, just south of Olivença, to the estuary of the Guadiana River, on the far South.


The undefined sector (Markers 802 to 899)

Due to the unresolved status of the Olivenza dispute (see Claims of sovereignty), a specific stretch of the Portugal–Spain border remains officially undefined and unmarked on the ground. When the Mixed Boundary Commission (Comisión Mixta de Límites / Comissão Mista de Limites) was tasked with surveying and placing the stone border markers following 19th-century bilateral treaties, operations were suspended along this sector of the Guadiana River.

Consequently, the boundary markers numbered from 802 to 899 were never installed. This leaves the border line completely untraced between the confluence of the Caia River (near Olivenza) and the confluence of the Cuncos Stream (Ribeira de Cuncos) with the Guadiana River. Official maps produced by both nations' geographical and military institutes reflect this anomaly through unique cartographic asymmetries. While Spanish topographies apply an alternate styling along the river axis that lacks the standard boundary shading seen elsewhere, official Portuguese military charts completely omit the international boundary line in this specific sector.

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