San Esteban de Deyo, also called the Castillo de Monjardín, is a ruined castle on a hill overlooking Villamayor de Monjardín in Navarre. The castle lies at an elevation of 890 metres. The castle has a Roman foundation, but was repeatedly rebuilt over the centuries. It was one of the last fortresses of the Banu Qasi, the local Muslim dynasty, before it was taken by King Sancho I of Navarre in 914. According to the Historia Caroli Magni et Rotholandi, the castle was actually taken by Charlemagne from a Navarrese prince named Furré. Only the walls of the castle stand today. Many of the stones were taken to build a Baroque hermitage, the Ermita de San Esteban, in the 17th century.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.