English: Castell de Sant Salvador, Sant Pere de Rodes, Catalonia, Spain, looking down to El Port de la Selva.

Inset: north tower. Lower section: aerial view of castle remains (on an information board at Sant Pere de Rodes monastery, below the castle).

From information boards at and near the castle:

"Verdera Castle stands at the highest point of the Sierra de Rodes, 670 metres (2000 feet) above sea level. Its summit provides an extraordinary panoramic view and it was this visual domination of the territory and its inaccessible site that gave it great strategic and military value in the Middle Ages.

"Built between the 9th century and the beginning of the 10th, the castle played an important part in a number of wars. Between the 14th and 15th centuries, thanks to the evolution in techniques of combat and the emergence of artillery, the fortress lost its military function and from the 16th century was used as a watchtower against pirate raids. It is one of the finest examples of military architecture of the time.

"The castle consists of a walled precinct inside which are the different quarters that housed the military garrison. The wall, which dates from the end of the 13th century, marks out the fortification only on the north-eastern side, as the others are protected by the cliffs. Along the wall a total of seven half towers are laid out, semicircular and rectangular alternately. To our left a large tower closes off the fortress to the north. The entrance to the castle was through a tower gateway at the north-eastern end. Inside the precinct the remains of different buildings are conserved, among them the Romanesque Sant Salvador church, a building with a basilica ground plan, three naves and an east end with three apses. Outside, near the entrance, is a cistern which supplied the garrison with water."

See also (in Catalan, with images):

www.catalunyamedieval.es/castell-de-sant-salvador-de-verdera-alt-emporda

ca.wikipedia.org/wiki/Castell_de_Verdera