The Château des ducs de Lorraine (Castle of Dukes of Lorraine or Sierck Castle) may have been a Gallo-Roman fort, but the first historical document of the castle date from 1067. However there is probably nothing left of this first castle. The current castle was built by the archbishop of Trier in the 15th century. French army conquered it in the 17th century and since 1661 it became part of the reign of France. The castle lost its defensive purpose and it was demolished in 1673. Later fortifications was re-enhanced and left to decay several times. In 1866 The Château was acquired by the city of Sierck les Bains.
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.