Gamleborg, also known as Gamleborg Viking Fortress, was the first fortress on the Danish island of Bornholm. Built around 750 AD, it was the seat of the kings of Bornholm during the Viking age (750–1050) and early Middle Ages (1050–1150). The massive fortress is 264 metres long from north to south and 110 metres wide from east to west, with gates to the north and southwest. Around 1100, significant alterations were made and it was reinforced, but it was abandoned soon afterwards in favour of Lilleborg Castle, roughly 700 metres to the northeast.
The fortress is Bornholm's oldest defence works. Its builder is unknown, but an account of the Baltic Sea travels of Wulfstan of Hedebyin 890 tells us that Bornholm already had its own king at the time. There is, however, firm evidence that the fortress was in use during the reigns of Harald Bluetooth (940–986) and Canute IV (1080–1086). The Gamleborg fort was used as refuge during the tenth century against Viking raids. Gamleborg was abandoned in 1150, the occupants moving to Lilleborg, only 700 metres to the northwest. It is not known why the move was made but it does not appear to have been the result of hostilities. Excavations in the 1950s showed the fortifications originated in the Viking period although there is evidence the site was used as a hideout in the Iron Age. The ruins that can be seen today are mainly the result of reconstruction work completed in about 1100.
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.