Žrnov (Serbian Cyrillic: Жрнов) or Žrnovan (Жрнован) was a medieval fortress on the highest top of the Avala Mountain, at 511 metres (1,677 ft), in Belgrade, Serbia. The Ancient Romans had built an outpost there, and later the Serbs expanded it into a fortress. It was completely demolished in 1934 to make the way for the Monument to the Unknown Hero.