This castle held the Coyanza Council in 1050; the old Coyanza was populated and fortified by Fernando II of León in the second half of the 12th century. The current castle was built in the 15th century. It was constructed on the site of older castle that had been erected on the ruins of a fortification dating back to the Iron Age.
The castle consists basically of one articulated front with projections, flanked by turrets overshadowing the tower of homage, with round turrets in the Gales and fronts.
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.