The foundation for Lohr Castle, first mentioned in records in 1389, was laid around 1340 by Count Gerhard V of Rieneck at the northwest corner of the old town of Lohr am Main. Initially, it was just a residential tower modeled after Flemish designs, which was surrounded by a moat and a ring wall from the late 15th century onwards. Nearby were buildings such as the bandhouse, forestry office, coach house, and cellar.
After the death of the last Count of Rieneck, Philipp III, the Electors of Mainz took over the building in 1559 as regional rulers and gradually gave it its present form. It became the seat of the Electorate's senior officials. The most well-known official was Philipp Christoph von und zu Erthal, who used the castle as his residence from his appointment in 1719 until his death in 1748. His two princely sons, Friedrich Karl Joseph von Erthal, one of the last Electors of Mainz and Prince-Bishop of the Diocese of Worms, and Franz Ludwig von Erthal, born in Lohr and later Prince-Bishop of Bamberg and Würzburg, were raised here.
In 1814, the Kingdom of Bavaria took over the castle and used it as an administrative seat. Among other things, it housed the district office of the Lohr district until the territorial reform of 1972. The building was renovated in 1913.
In the castle's Knight's Hall, the Lohr Museum of Local History and the Spessart Museum were established in 1936. The museum was closed in 1942 and reopened in 1949. Since 1972, only the Spessart Museum remains in the building, focusing on the history of the castle and the Spessart region, with an emphasis on the relationship between people and the forest.
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.