451: Battle of the Catalaunian Plains: Roman and Visigoth forces defeat Attila the Hun in northeast France, halting the Hun invasion of Roman Gaul [exact date disputed]

1789: French Revolution: The Third Estate of the French Estates-General swears the Tennis Court Oath at the Palace of Versailles, vowing not to disband until a new constitution is formed

1840: American inventor Samuel Morse receives a patent for his telegraph

1895: First woman to earn a PhD in Physics from an American university, Caroline Willard Baldwin (25), receives her degree from Cornell University

2020: Highest-ever temperature recorded in the Arctic Circle, 38°C (100°F) in Verkhoyansk, Siberia

Source: Onthisday.com