Wikipedia:Selected anniversaries/September 20
- 1378 - Papal Schism: Unhappy with Pope Urban VI (pictured), a group of cardinals started a rival papacy with the election of Antipope Clement VII, throwing the Roman Catholic Church into turmoil.
- 1854 - The Crimean War began with a Franco-British victory over Russian forces in the Battle of Alma.
- 1870 - The Bersaglieri entered Rome, ending the temporal power of the Pope and completing the unification of Italy.
- 1906 - The ocean liner RMS Mauretania, the largest and fastest ship in the world at the time, was launched in Newcastle, England.
- 1973 - Billie Jean King defeated Bobby Riggs in straight sets before 30,492 spectators at the Astrodome in Houston, Texas in an internationally televised tennis match dubbed the "Battle of the Sexes".
Recent days: September 19 – September 18 – September 17
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