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:Trenčín Castle is relatively large renovated castle, towering on a steep limestone cliff directly above the city of Trenčín. It is a dominant feature not only of Trenčín, but also of the entire Považie region. The castle is a national monument.
History of the castle cliff dates back to the Roman Empire, what is proved by the inscription on the castle cliff proclaiming the victory of Roman legion against Germans in the year 179.
Today’s castle was probably built on the hill-fort. The first proven building on the hill was the Great Moravian rotunda from the 9th century and later there was a stone residential tower, which served to protect the Kingdom of Hungary and the western border. In the late 13th century the castle became a property of Palatine Matúš Csák, who became Mr. of Váh and Tatras.
Matúš Csák of Trenčín built a tower, still known as Matthew’s, which is a dominant determinant of the whole building.