Boppard’s most famous sight is a castrum, a Roman Fort. The military camp of Bodobrica was established here in 360 AD. It is thought to be the best preserved example north of the Alps today. It once had 28 towers, and was a commercial centre as well as a fort. It was 308 × 154 metres and formed a rectangle of 4,7 hectare. The walls were 3 metres thick to the land side and 2,5 metres thick to the Rhine side. With a height of 9 metres and 20 horse-shoe shaped towers to the land side, each 27 metres apart, the wall made a very powerful fortification.
The fort can be wandered around freely and it is in remarkably preserved condition. Many of the finds that have been recovered and excavated from the site can be found in the Boppard museum.
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.