It is not known exactly when the Tiefburg castle was built or by whom. It is assumed that it was built in the 12th century, possibly by the Abbey of Lorsch or the Count Palatinates of the Rhine (later known as the Prince Electors of the Palatinate), who set up residence in nearby Heidelberg around this time. It is also possible that the castle had its origins in a fortiied estate. The knights of Handschuhsheim who lived in the Tiefburg were initially unfree knights, known as ministeriales, in the service of the Abbey of Lorsch, and later on vassals of the Prince Electors of the Palatinate. The dynasty died out when the last knight of Handschuhsheim, Johannes (Hans) V., died aged 16 on 31st December 1600 from injuries sustained in a duel. Through inheritance, the Tiefburg became the property of the barons of Helmstatt (who became counts of Helmstatt in the 18th century).
Tiefburg was badly damaged in the Thirty Years‘ War. In 1689 it fell victim to the War of the Palatine Succession and became uninhabitable, whereupon the Helmstatts built a new residence in the immediate vicinity. The original gate of this new residence can still be seen to the east of the square in front of the Tiefburg. Count Raban von Helmstatt had the Tiefburg restored in the years 1910 to 1913.
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.