Wikipedia:Selected anniversaries/July 3
- 323 – Roman Emperor Constantine I defeated colleague Licinius in the Battle of Adrianople.
- 987 – Hugh Capet was crowned King of France, becoming the first monarch of the Capetian dynasty, which ruled France until the French Revolution in 1792.
- 1608 – Quebec City was founded by Samuel de Champlain.
- 1863 – Pickett's Charge occurred during the final and bloodiest day of fighting in the Battle of Gettysburg, marking a turning point in the American Civil War.
- 1938 – The LNER Mallard (pictured) reached a speed of 203 km/h (126 mph), a world record for a steam railway locomotive.
- 1964 – President Lyndon Johnson signed the Civil Rights Act of 1964, prohibiting racial segregation in public places in the United States.
- 1988 - United States Navy warship USS Vincennes shot down Iran Air Flight 655 over the Persian Gulf, killing all 290 people aboard.