📅 Today in HistorySeptember 21

Emperor Avitus enters Italy with a Gallic army and consolidates his power.

Anglo-Norman invasion of Ireland: The Kingdom of Dublin falls to Anglo-Norman invaders.

Livonian Crusade: The Estonian leader Lembitu and Livonian leader Caupo of Turaida are killed in the Battle of St. Matthew's Day.

The Treaty of Arras is promulgated, causing Burgundy to switch sides in the Hundred Years' War.

A British government army led by Sir John Cope is defeated in less than 15 minutes by the Jacobite forces of Prince Charles Edward Stuart.

Part of New York City is burned shortly after being occupied by British forces.

American Revolutionary War: Benedict Arnold gives the British the plans to West Point.

French Revolution: The National Convention abolishes the monarchy.

British Secretary of War Lord Castlereagh and Foreign Secretary George Canning meet in a duel on Putney Heath, with Castlereagh wounding Canning in the thigh.

War of 1812: British forces abandon their unsuccessful siege of Fort Erie.