What is "zrnov"

Žrnov or Žrnovan was a medieval fortress 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 captured the fort, and expanded and strengthened it for preparations of the attack on Belgrade, based on the orders of Sihàb ed-Dîn Pasa, eunuch beylerbey of Rumelia Eyalet. 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 site for the construction of Mausoleum Monument to the Unknown Hero, whose author was the sculptor Ivan Meštrović.