Ćele Kula [tɕel̩e kula] (Serbian Cyrillic Ћеле-кула, German Skull Tower) is a tower in the Serbian city of Niš. It was built by the Ottomans from the bones and skulls of Serbian rebels who fell at the Battle of Čegar during the First Serbian Uprising on May 31, 1809. The French writer Alphonse de Lamartine (1790-1869) described the tower in his book Voyage en Orient, in which he addressed the atrocities committed by the Ottomans against the Serbian population.
Source: Wikipedia