The Friedberg castle was subsequently built to serve as a border security and customs post for the Duchy of Bavaria and Swabia, but put the town in opposition to the free city of Augsburg. It was built between 1257-1264 by Duke Ludwig II.
The castle was the cause of the first burning of Friedberg by Augsburg in 1396. The town was subject to the many frequent wars between Swabia, Bavaria and Augsburg.
A revival in the town's fortunes came when, in 1568, the Duchess Christine chose Friedberg castle as her seat following her husband's death. The town became the centre of Bavarian court life, but was short lived when the town was ravaged by the plague in 1599. More suffering came as the town was sacked twice by the Swedes during the Thirty Years War. After the war only the town hall, castle and city walls were left standing.
The castle is situated on a spur of and has an unusually deep moat. Since the renovation in 1982, Friedberg castle has been a museum.
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.