The Castle of Gormaz, in the province of Soria, Spain, is strategically situated on a high promontory overlooking the small Castilian village, San Esteban de Gormaz, and the Duero River with its expansive flatlands. It was constructed in 956 under the reign of caliph Al Hakam al-Mustansir, (Al-Hakam II) to further fortify Moorish territory and as a base for military offenses into northern territories. The oldest and largest citadel in Western Europe, it measures 390 meters in length and up to 60 meters in width.
Built with ashlar carved stone.Divided into two areas by a moat:the
fortress and the walled enclosure where the soldiers and the cisterns
were.In the fortress there were seven towers out of which the Almanzor
and the Keep are the most noteworthy.It also had an underground
reservoir and an important armoury. (http://www.spain.info/en_US/que-quieres/arte/monumentos/soria/castillo_de_gormaz.html)
Its most prominent detail is its original entrance that features a double horseshoe arch. After being repeatedly sacked by both Arab and Christian armies
throughout its early history, it now remains unused and in the property
of the local municipality.