- 1478 Pazzi conspirators attack Lorenzo de’Medici and kill Giuliano de’Medici in Florence
- 1920 Harlow Shapley and Heber D. Curtis hold “great debate” on the nature of nebulae, galaxies and size of the universe at US National Academy of Sciences, Washington, D.C.
- 1945 Marshal Philippe Pétain, leader of France’s Vichy collaborationist regime during World War II, arrested for treason
- 1956 First modern container ship, the Ideal X, leaves Port Newark, New Jersey for Houston, Texas
- 1986 World’s worst nuclear disaster: 4th reactor at Chernobyl nuclear power station in USSR explodes, 31 die, radioactive contamination reaches much of Western Europe
- 2005 Under international pressure, Syria withdraws the last of its 14,000 troop military garrison in Lebanon, ending its 29-year military domination of that country.