After the fall of Constantinople in 1453, the Ottoman Sultan Mehmed the Conqueror rallied his resources to subjugate the Kingdom of Hungary. His immediate objective was the border fort of the town of Belgrade. John Hunyadi, the Count of Temes and captain-general of Hungary, who had fought many battles against the Turks in the previous two decades, prepared the defenses of the fortress.

The siege escalated into a major battle, during which Hunyadi led a sudden counterattack that overran the Ottoman camp, ultimately compelling the wounded Mehmed II to lift the siege and retreat. The battle had significant consequences, as it stabilized the southern frontiers of the Kingdom of Hungary for more than half a century and thus considerably delayed the Ottoman advance in Europe.

As he had previously ordered all Catholic kingdoms to pray for the victory of the defenders of Belgrade, the Pope celebrated the victory by making an enactment to commemorate the day. This led to the legend that the noon bell ritual undertaken in Catholic and old Protestant churches, enacted by the Pope before the battle, was founded to commemorate the victory. The day of the victory, July 22, has been a memorial day in Hungary ever since.