Wikipedia:Selected anniversaries/September 20
- 451: Flavius Aëtius, with the help of Roman foederati, defeated Attila in the Battle of Chalons, and halted the invasion of Gaul by the Huns and their allies.
- 1378: Papal Schism: Unhappy with Pope Urban VI, a group of cardinals elected a rival papacy in Antipope Clement VII, throwing the Roman Catholic Church into a turmoil.
- 1854: The Crimean War began with a Franco-British victory over Russian forces in the Battle of Alma (pictured).
- 1946: The first Cannes Film Festival opened. The Palme d'Or, then known as the Grand Prix du Festival, was shared by eleven films that year.
- 1973: Billie Jean King defeated Bobby Riggs in straight sets in an internationally televised tennis match dubbed the "Battle of the Sexes".
Recent days: September 19 – September 18 – September 17
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