Bagacum (Today Bavay) was an Roman city and remarkable remains of ancient forum still exist. The 2,5 hectare are contains ruins of a central esplanade, temple and cryptoporticus (covered corridor or passageway).
The birth of Bavay after the conquest was the result of the reorganization of the territory by Augustus (probably between 16 BC and 13 BC). The town became the capital for the Nervii under the name of Bagacum and was an important junction of seven roads, the meeting-place of which was marked by a milestone, destroyed in the 17th century and replaced in the 19th century by a column.
From the Claudian period and especially under the Flavians in the late 1st century the city grew. Large monuments were built: a forum, thermal baths fed by an aqueduct bringing water from a fountain near Floursies located twenty kilometres away, and other buildings with a seemingly official nature adorned the city.
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.