Wikipedia:Selected anniversaries/May 18
- 1268 - Baibars and his Mamluk forces captured Antioch, capital of the crusader state, the Principality of Antioch.
- 1896 - "Separate but equal": The U.S. Supreme Court ruled in the landmark case Plessy v. Ferguson, upholding the legality of racial segregation in public transportation.
- 1944 - World War II: Polish forces under Lieutenant General Władysław Anders captured Monte Cassino and broke the Winter Line, a German defensive line in Italy.
- 1958 - The F-104 Starfighter, a supersonic interceptor aircraft, set a world speed record of 1,404.19 mph.
- 1980 - Mount St. Helens erupted (pictured), killing 57 people in southern Washington State and causing over a billion U.S. dollars in damages.