Roman Emperor Valentinian I made his brother, Flavius Valens, his co-emperor.
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Frenchman Henri Fabre flew the world's first seaplane in Martinique, France.
The Treaty of Florence was signed, which ended the war between the French Republic and the Kingdom of Naples.
The Vienna Philharmonic Orchestra performed its first concert.
A nuclear disaster occurred at Three Mile Island in Pennsylvania, US.
The world's first weightlifting championship took place in London, England.
