Although Siersberg Castle was first mentioned in 1178, it was probably already built in the 11th century. It was built atop an almost 300-meter-high mountain overlooking the valleys of the rivers Saar and Nied.
During the Thirty Years' War, in 1634, the castle was taken by French troops. In the next decades it was taken and retaken several times by both parties, which of course caused damage to the castle. In 1670 the French again occupied Lorraine. When they retreated again in 1677 they partly blew up the, by then already dilapidated, castle. After that, Sierberg increasingly lost its military importance and its decay progressed.
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.