The Castillo de Portillo is a well-preserved medieval castle in Portillo; the earliest elements of its present construction date to the fifteenth century. The site has been fortified since the tenth century, when it is documented in connection with Moorish forays into the region, under Abd al-Rahman III. In the fourteenth century, and until the early fifteenth, it was in the possession of the family of Sandoval; in 1392 it was confiscated from Diego Gómez de Sandoval in the name of King Juan II of Castile, who granted it in 1438 to Ruy Díaz de Mendoza.
From 1448 to 1452, Portillo was occasionally held by Juan's favourite, Don Álvaro de Luna, although the fortress remained in royal hands. Don Álvaro, however, fell from favor, and was detained at Burgos, sent to Portillo until two months later he was tried at Valladolid, and subsequently beheaded in the main Plaza on 2 June 1453. In 1464 Enrique IV of Castile conferred it upon Alfonso, held in trust by Juan Pacheco, the prince's tutor, until his death (1474), though it had been ceded to Rodrigo Alfonso de Pimentel, whose heirs held it until the nineteenth century, when it passed to the family of Osuna.
As the history above indicates, Portilla is better known for the list of distinguished prisoners it has housed, than for being the site of battles or other events. Juan II of Castille was briefly imprisoned at Portillo in 1444 by the Conde de Castro, escaping by bribing one of his guardians. The chronicles also touch upon the fact that Don Enrique, brother of the admiral Don Fabrique y de Suero de Quiñones (who fought at Paso Honroso) was jailed here for conspiring against the crown.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.