1478 – In a conspiracy to replace the Medici family as rulers of the Florentine Republic, the Pazzi family attacked Lorenzo de' Medici and killed his brother Giuliano during High Mass at the Florence Duomo.
1564 – Playwright William Shakespeare is baptized in Stratford-upon-Avon, Warwickshire, England (date of actual birth is unknown).
1933 – The Gestapo, the official secret police force of Nazi Germany, is established.
1956 – SS Ideal X, the world's first successful container ship, leaves Port Newark, New Jersey for Houston, Texas.
1986 – The Chernobyl Nuclear Power Plant near Chernobyl, Ukrainian SSR, suffered a steam explosion, resulting in a fire, a nuclear meltdown, and the evacuation and resettlement of over 336,000 people around Europe.