Upon being viewed by the sultan, the skulls were then returned to Niš, where the Ottomans built Skull Tower as a warning to non-Muslim residents contemplating rebellion.[5] The Ottoman Empire was known to create tower structures from the skulls of rebel fighters in order to elicit terror among its opponents.[7] Skull Tower was constructed on the road from Istanbul to Belgrade.[8] It was built of sand and limestone.[9] The structure is 4.5 metres (15 ft) high.[10] It originally consisted of 952 skulls embedded on four sides in 14 rows.[5] The locals named it ćele kula, from the Turkish kelle kulesi, which means "skull tower".[3]