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