The top of the Avala mountain proved to be suitable for building, so the Romans built a fortified outpost, probably on the foundations of the older Celtic one. Apart from guarding and controlling the access roads to Singidunum, the outpost was also important for the protection of the numerous mines on the mountain, which were exploited by the Romans. They were extracting lead, zinc, silver and mercury, close to the modern Ripanj. The outpost was some below the top of the mountain. The outpost was a base for the future medieval fortress of Žrnov.