Fort Šibeník The main task of the building was to advance the defence of the bastion fortress on its western side and at the same time to prevent an attack on the town from the Šibeník Hill. The massive lunette-shaped fortress was made up of four lines of defence separated by a dry moat. The outer defensive line was a front line with a covered road. This line included an underground system of brick mine tunnels. Fort Šibeník Hill is held by a private entity.