Neither the origins nor the date of construction of San Romualdo Castle is certain, although historians are fairly sure that this castle dates back to medieval times. Built in the Mudéjar style, it was first mentioned in 1268. It is thought to have been used as both convent and fortress.
The castle was officially declared as a historic monument by the Spanish authorities in 1931 and is easily located near the town centre, half way between the town hall and the Zuazo Bridge.
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.