Žrnov or Žrnovan (Жрнов) was a medieval fortress located on the highest top of Avala, at , in Belgrade, Serbia. At the top Ancient Romans built the outpost, and later the Bulgarian and the Serbs expanded it into a fortress. Ottomans occupied fort, and expanded and strengthened it for preparations of the attack on Belgrade. In the city, according to legend dwelt, celebrated in songs, Porča of Avala. The remains of the fortifications was demolished by dynamite in 1934, in order to clear the cite for the construction of Mausoleum Monument to the Unknown Hero, whose author was the sculptor Ivan Meštrović.