Fortress Kastel is the oldest historical monument in the City of Banja Luka. The oldest traces of settlements on the territory of Banja Luka are the remnants of Neolithic settlement that were exactly found on the territory of the city fortress Kastel. It is found in the central part of the city, which dominates over the left bank of the river Vrbas.
In the past Kastel was a strong army fortification and it protected the basin of the river Vrbas from enemy rush. The fortress is surrounded by thick stone walls on all sides, and in its inner part, apart from the summer stage, playground for children and national restaurant, there is the Institute for protection of cultural and natural heritage of the Republic of Srpska that works from 1976. There are no confident data on the period of foundation of this object.
However, many circumstances point to a conclusion that exactly on this location there was a Roman settlement Castra. The Romans were exposed to frequent rushes of barbarian nations, and they had strong reasons to defend the road that passed through the basin of the river Vrbas. On behalf of such statements there are archaeological findings that were discovered on the territory of current Kastel, and it refers to the Roman ceramics, money and architecture.
A particularly important finding is the antique altar dedicated to the God Jupiter, found in 1885 during the construction of the bridge across the river Crkvena. Further on, on the territory of the fortress remnants of the Slavic settlements from the period of early Middle Age were found (from VIII to XII century). In the Bosnian medieval state there was a Vrbas city, which, according to an assumption, was located on the position of current Kastel. Still, according to the other assumption, the Vrbas city is identified with Podgradci in Potkozarje.
Intensive construction of Kastel begins in the last but one decade of the 15th century, in the period of Turkish occupation and the reign of the dynasty of Ferhad pasha Sokolović(1574-1588) that apart from this fortification built series of other objects of oriental type. Ferhad-pasha firstly built his fortified tophane (arsenal) on the place of current Kastel, in order to, in some ten years later, turn the tophane into real fortified city with towers and tabiyas, which was constantly additionally built. Since it lies on the mouth of Crkvena into Vrbas, two bridges were constructed from the fortress.
One lied across the river Vrbas, near the current city bridge, and the other across the river Crkvena. The bridge across the river Vrbas is saved only in one of the old engravings. The rivers Vrbas and Crkvena were connected by one huge retrenchment (ditch) so that the fortress was actually, at the time, a fortified isle surrounded by the waters of the two rivers.
On the walls of the fortress there was also a large wooden billet that looked out to the river Vrbas, as well as the series of built objects from the period when the Austro-Hungarian army was in the fortress. The fortress, as well as the City of Banja Luka, especially gained on the significance in the period of the Austro-Hungarian-Turkish wars as an important geostrategic center. In the plans for recovery, restoration and revitalisation of Kastel it was anticipated that one part of these objects be restored, so that the fortress could have the appearance as similar as it was possible to the old one. At the area of the fortress itself, a great variety of archaeological traces were found, from antique period, over the mentioned Slavic settlement, to newer cultures.
The Roman sarcophagus, the Roman milestone from the old road Salona – Servitium, which was found in Šargovac, can be found on Kastel. Today Kastel is a monument of the first class and a place where you can experience the spirit of the past time.