Holsterburg was built by brothers Hermann and Bernhard Berkule before 1191. It was destroyed in local war in 1294. After its destruction, the Holsterburg was covered with a mound of earth, probably also for symbolic reasons, to erase the Berkule family and their ancestral seat from the memory of posterity. Under the hill, the complex has been preserved as it was in 1294.
The hill was excavated in 2010-2017 and castle ruins were cleaned.
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.