The Cyriaksburg Fortress is situated on a hill outside the city gates of Erfurt. The construction was started in 1480 but not completed until about 1604. The shape of the foundations is like a rectangle with unequal sides. Two strong round towers from 1528 have been preserved. One of them is now used as a viewing tower and the other one houses an observatory. The moat is also partly visible.
From 1631 to 1649, during the Thirty Years' War, Cyriaksburg was occupied by the Swedes. During that time it is said that the famous physicist Otto von Guericke from Magdeburg assisted in fortifying parts of the castle. The remains visible today date back mainly to 1824 until 1830, when the Prussians converted the castle into a fortress. The underground parts house a well of about 40 metres depth for drinking water and for water to extinguish fires. This well dates back to 1530. The brick vaults above the well date back to 1829.
Parts of the fortress were dismantled between 1874 and 1900. The surrounding areas were gradually planted with shrubs and flowers and opened to the public. The rooms of the Cyriaksburg Castle are now used for the permanent exhibition of the German Museum for Horticulture.
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.