Banja Luka is the second largest city in Bosnia and Herzegovina after the capital Sarajevo and is the largest city of the Republika Srpska.
The Roman trade route from Salona to Servitium passed through it and to protect this route the Romans built a fortress here. After the Romans, the Slavs took over the city in 7th century and then it fell to the Ottomans in 1527. In the Ottoman time Banja Luka was repeatedly destroyed by Ottoman-Habsburg warfare. It was absorbed peacefully by Austrian-Hungarian Empire in the 19th century.
I believe that Banja Luka deserves much more attention than we were able to give it during our journey. However, when we arrived there was still a long drive to Sarajevo ahead of us, so we could only stay there for a couple of hours.