As early as the 12th century there was a small predecessor castle on the site of a former Roman villa rustica from the 2nd to 4th century in the present village of Welschbillig.
From 1242 to 1299 the fortifications of the castle were significantly strengthened by the Prince-Elector of Trier, Arnold II of Isenburg and, later, the Landesburg was further expanded by his successors. During the so-called Dutch War the castle was destroyed in 1673/74 by troops of the French 'sun king' Louis XIV and from 1889 to 1891 the southern side was demolished to build a church.
The castle built over the remains of the Roman villa survive today as the remains of a large, quadrangular castle with moats. Still visible are the gateway with its two round towers, a stone bridge over the moat and the remains of the northwest tower.
The Roman villa was built in the shape of the letter 'U' next to a 58.3 by 17.8 metre water basin, which was originally surrounded 112 hermas. 71 of the hermas may be seen in the Rheinisches Landesmuseum Trier.
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.