The Archbishops of Mainz had the Mildenburg castle built at the end of the 12th century to secure their powerful position and to serve as a customs office. Around 1200, the castle keep was added, the first official reference dates to 1226. Rather diverse periods in history affected the castle: extending, capturing, damaging and reconstructing.
Mildenburg the seat of the Oberamtmann, the Archbishop's local administrator until 1803. It then passed to the Princes of Leiningen before Carl Gottlieb Horstig purchased it in 1825. It now houses a museum of icons and contemporary art. The castle’s inner ward once held the Teutonenstein, a 5 m-tall sandstone column found on Greinberg, the inscription of which is still a puzzle to this day.
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.