The following is a sidebar to this post I have written for Samizdata
Portugal has existed as a state since Afonso Henriques, Count of Portugal, achieved independence from the Kingdom of Leon (one of the four kingdoms generally considered the predecessors of modern Spain) and declared himself King Alfonso I of Portugal in 1139. At that point Portugal only consisted of the North of the modern country, but Alfonso pursued a series of conquests that expelled the Moors from much of the south of the modern country. Olivenca fell to Alfonso in 1170, but was retaken by the Muslims in 1189. In 1230, Olivenza was taken from the Moors by the Knights Templar in 1139, ultimately being absorbed into the Kindom of Castille, predecessor to modern Spain. It was reclaimed by Portugal in 1297, during the succession crisis following the death of King Sancho IV of Castille, Leon, and Galicia. Olivenca then remained Portuguese for more than 500 years, although Portugal was in Personal Union with Spain (ie the same king ruled two multiple kingdoms that were theoretically separate) from 1580 to 1640.

In 1373, Portugal signed a treaty of perpetual friendship with England, that remains in force to this day. In 1510, the Ajuda bridge was built across the Guardiana river to the nearby Portuguese town of Elvas. In the war of Spanish succession (that took place between 1701 and 1714), Portugal sided with the British and Prussians against the Spanish and French, in accordance with the treaty of 1373. Olivenca was held by Portugal, but there was fighting in the area and the Ajuda bridge was damaged and made impassable in 1709.