At the end of the 3rd century Arlon was fortified with the construction of ramparts. This castrum was 800 metres in circumference with walls that were 4 metres thick and 8 metres high with two gateways and around 20 watch towers. The Neptune tower was identical to the Jupiter tower recently discovered near to the Town Hall. The small museum consists of remains of the tower which were discovered during archaeological excavations in 1948. In the foundations of the wall one can see various sculpted stones from the ancient vicus including asuperb bas-relief representing Neptune. To visit the Neptune Roman Tower, a key can be obtained from Maison Knopes, 24 Grand Place.
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.