The Monument to the Unknown Hero (Serbian Cyrillic: Споменик Незнаном јунаку, romanized: Spomenik Neznanom junaku) is a World War I memorial located atop Mount Avala, south-east of Belgrade, Serbia, and designed by the sculptor Ivan Meštrović.

[1] On the night of 13/14 October 1915, Combined squad of the Belgrade's Defense, held the line Avala-Zuce, defending it from the joint Austro-Hungarian and German offensive.

Austro-Hungarian 9th Hill brigade of the 59th Division took the front rim of Avala on 16 October, with an assignment to push Serbian forces from the mountain.

On the same day, the command of the Belgrade's Defense ordered the retreat to the new positions so on 17 October occupational forces reached the southern section of Avala, conquering the entire mountain.

In the valley, below Žrnov, on the grave of one of them, they placed a wooden cross with the inscription in German: "One unknown Serbian soldier".

As the French influence was very strong on Serbian army since the mid-19th century, the idea of doing the same spread among the veterans and social associations, reaching the National Assembly.

On 24 June 1921, president of the Constitutional Assembly, Ivan Ribar, summoned state dignitaries to the meeting with the agenda of constructing the monument.

Parts of the grenade are found under the skull, almost as a pillow, while the skeleton had the blown left side of the chest, so it is estimated that he was killed by the Austro-Hungarian howitzer while he was watching from the lookout.

The boots were American, M-1910, mostly distributed to the members of the Personnel department and, to a lesser extent, to the regiments of the First Call (which drafted the youngest soldiers, up to 31 years old).

[2][4][5] The Assembly Board organized many events in 1922 in order to gather the funding for the monument, but also used the other means for the promotional purposes, like the cinema shows.

Also, some more prominent events are used, like the Christmas money collecting by the Patriarch Dimitrije or the wedding of King Alexander I and Queen Maria on 8 June 1922.

On the eastern side of the pedestal a plate was placed with the inscription: "To the fallen heroes in the wars for liberation and unification 1912–1918, this monument is erected by the thankful people of the Vračar District.

On the western side of the horizontal arm of the cross another inscription read: "Unknown Serbian soldier confirmed by the commission on 29 November 1921".

Among the dignitaries at the dedication of the monument were Ivan Ribar, other senior politicians from the Assembly, presidents of the surrounding municipalities and districts and several government ministers.

The old monument was completely demolished, except for the six-armed cross which was moved to the churchyard of the Church of Saint Mary Magdalene in Beli Potok, where it is still located.

[9] Before the construction of the new monument started in 1934, the ancient fortified town of Žrnov was located atop the Avala mountain.

Ironically, on that section of the square, today known as the Plateau of Zoran Đinđić, actually the monument to Branislav Nušić was erected.

King Alexander wanted to transform the top of the Avala into the replica of the Kajmakčalan mountain which gained almost mythical importance after the 1916 Battle of Kaymakchalan between Serbia and Bulgaria, and was euphemistically called "Gate of the Homeland" or the "Altar of the Motherland".

[2] Several historians from Belgrade and Sarajevo have claimed that the unknown hero is a Bosniak named Sulejman Balić, a soldier from Duga Poljana, a town between Novi Pazar and Sjenica, that fought in the Royal Serbian Army against Austria-Hungary.

[5] But as the evidence suggest, the soldier was drafted immediately prior to the Central Powers offensive in October 1915, as he didn't receive the ID badge, so this claim is unlikely.

[4] Hastiness by which the Žrnov was demolished and king Alexander's insisting on building the monument on this location despite all the opposition, in time influenced numerous conspiracy theories.