The castles in Spain were built mainly for the country's defense, particularly with respect to fortification. During the Middle Ages, northern Christian kingdoms had to secure their borders with their Muslim southern neighbours, thus forcing both Christian and Muslim kings to grant border fiefs to their liege noblemen so as to keep and maintain defensive fortresses. When the Reconquista advanced, those border castles lost their initial purpose, and, as in the rest of medieval Europe, they were used as noble residences and fief-keeps. Sporadic threats of war maintained their initial military purposes as enemy invasions were common. In some locations, such as the Basque country, fiefdoms did not exist as such, and noble families could not afford nor did they need huge fortresses, giving rise to many tower houses. In Muslim Spain many castle-palaces were built: the petty taifa kingdoms that arose after the fall of the Caliphate of Córdoba were militarily weak thus castles began taking on a more aesthetic purpose. During the late Middle Ages, Christian kingdoms had secured and enriched themselves well enough to support a more courtly lifestyle, so more residential castles were built, such as the Alcázar of Segovia, which was used as the main residence of the kings of Castile, whereas the Castle of Olite, built in a luxurious gothic style, was the seat of the Kingdom of Navarre's royal court. After the Conquest of Granada in 1492, the Catholic monarchs ordered all the castles in their realms to be handed over to the Crown. Although the order was not completely carried out, the War of the Germanias, a rebellion against king Charles V in the early 16th century, forced the new Spanish Habsburg dynasty to continue the process, and many castles were demolished as well. Most of the castles in Spain were successively abandoned and dismantled, Spanish kings fearing noble and peasant revolts, especially in the newly conquered lands. Accordingly, some of them are nowadays in a state of decay, and although some restoration work has been done, the number of former castles is so large that the Spanish government lacks both the resources and the will to restore them all.

Andalucía

Almería

Cádiz

Córdoba

Granada

Huelva

Jaén

Málaga

Sevilla

Aragón

Huesca

Teruel

Zaragoza

Principality of Asturias

Basque Country

Araba

Gipuzkoa

Biscay

Balearic Islands

Canary Islands

Cantabria

Castile and León

Ávila

Burgos

Leon

Palencia

Salamanca

Segovia

Soria

Valladolid

Zamora

Castile-La Mancha

Albacete

Ciudad Real

Cuenca

Guadalajara

Toledo

Catalonia

Barcelona

Tarragona

Girona

Lleida

Extremadura

Cáceres

Badajoz

Galicia

A Coruña

Lugo

Ourense

Pontevedra

Community of Madrid

Region of Murcia

Navarre

La Rioja

Valencian Community

Alicante

Castellón

Valencia

Number of fortifications by provinces

In the following table, are related the various Spanish provinces, ordered according to the number of existing fortifications, both castles themselves as towers, watchtowers, bunkers, walls and castros It attached the references to some of the relevant statements of Cultural Assets of the different Councils of Culture of the Autonomous Communities: