Fortress Kastel is located in Banja Luka and it is the oldest historical monument in this city. It was built on the left bank of Vrbas, between today's City Bridge and the crossing of the river Crkvena. In the past, Kastel was a strong military fortification and protected the Vrbas basin from enemy raids, primarily from the north. The fortress is surrounded by thick stone walls on all sides, where loopholes and observation posts are built. In the area of the fortress itself, a lot of archaeological traces have been found, from ancient times, through Slavic settlement to newer cultures. In Kastel, there is a Roman sarcophagus found in Šargovac, a Roman milestone from the former Salona-Servitium road. Today, at the site of the battle, many cultural events are held. There are numerous concerts and festivals held in the fortress, and some of them have become part of the manifestation tourism such as Demo fest and Fresh Wave.