Nitra castle was built in the 11th century on the place of an earlier fort. The core of the castle is St. Emmeram's Cathedral with the Bishop's residence, with several different parts. The oldest surviving part is the Romanesque Church of St. Emmeram from the 11th century. The other two parts of the cathedral are the originally Gothic Upper Church from the 14th century, and the Lower Church from the 17th century. Vazil´s Tower is another remaining part of the medieval fortification. According to a legend, Vazil, king Stephen´s nephew, was imprisoned in a dungeon supposed to be in the Tower´s underground.
The originally Gothic Bishop's Palace got its present Late Baroque appearance in the 18th century. There are also surviving parts of the castle fortifications, the majority of which were created in the 16th and 17th centuries and smaller part from the Middle Ages. The church is currently being remodeled.
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.