Wikipedia:Selected anniversaries/April 12
April 12: Cosmonautics Day in Russia, Yuri's Night.
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- 1204 – Alexios V fled Constantinople as forces under Boniface the Marquess of Montferrat and Enrico Dandolo the Doge of Venice entered and sacked the Byzantine capital, effectively ending the Fourth Crusade.
- 1606 – A royal decree established the Union Flag (pictured) to symbolise the Union of the Crowns, merging the designs of the Flag of England and the Flag of Scotland.
- 1861 – Confederate forces began firing at Fort Sumter in the harbor of Charleston, South Carolina, starting the American Civil War.
- 1927 – Chinese Civil War: A large-scale purge of communists from the nationalist Kuomintang began in Shanghai.
- 1961 – Aboard Vostok 3KA-2, Soviet cosmonaut Yuri Gagarin became the first man to enter outer space, completing one orbit in a time of 108 minutes.