Castillo de Aguilar is known from at least the 9th century. It is mostly in ruin, a part turned into a cistern for the local aqueduct. In the 9th century Aguilar de la Frontera became the headquarters of the rebel Umar ibn Hafsun, who built extensive fortifications and reinforced the castle. However, in 891, Umar ibn Hafsun lost the town to emir Abdallah ibn Muhammad of Córdoba. Due to its strategic position, it was contested and, after the dissolution of the caliphate of Córdoba, it became part of the cora of Cabra.
In 1240 it was conquered by the Christians, although numerous Muslims were allowed to remain. King Peter I of Castile assigned its seigniory to Alfonso Fernandez Coronel, but later reannexed it to the crown. The town was renamed Aguilar of the Frontier due to its position on the border with the Moorish Kingdom of Granada.
Since the mid-seventeenth century the castle was no longer needed for defense, consequently in 1860 it was converted into a Hospital. The Lisbon earthquake in 1755 caused part of the building to collapse. The fallen stones were reused for various public and private works. The remains of the castle are located on the hill to the north of the town on the extension of Calle Villa. The Tourist office is located at the castle. Free guided tours available on request.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.