| 3 September 863 | Arab Caliphate, Byzantine Empire [wars] | Petronas, the uncle of the Byzantine emperor, Michael III, annihilates an Abbasid army which has invaded Anatolia. The Abbasid general Omar is killed in the battle, which ends the Arab threat to the Byzantine Empire. |
| 3 September 1054 | Spain, Castile, Navarre [wars] | Ferdinand I of Castile defeats and kills his brother García III of Navarre at Atapuerca, near Burgos, Spain. Garcia's son Sancho IV succeeds as king of Navarre. |
| 3 September 1189 | England [political events] | Richard I the Lionheart is crowned as king of England; this date becomes the limit of legal memory (from 1290). |
| 3 September 1402 | Milan, Holy Roman Empire, Italy, Florence [political events] | When Gian Galeazzo Visconti, duke of Milan, dies, he is succeeded by his son, Giovanni Maria, with a regency. His death leads to the break out of anarchy in Lombardy, northern Italy, while the war against Florence ends. |
| 3 September 1651 | UK, France [British Civil Wars (1642–51)] | English supreme commander Oliver Cromwell defeats King Charles II at the battle of Worcester, England. Charles subsequently escapes, arriving in France in mid-October. |
| 3 September 1658 | England [administration] | Following the death of Oliver Cromwell, he is succeeded as Lord Protector of England by his son Richard. |
| 3 September 1658 | England, Scotland, Ireland [births and deaths] | Oliver Cromwell, English soldier and statesman, commander of Parliamentarian forces in the English Civil Wars (1642–51), Lord Protector of England, Scotland, and Ireland 1653–58, dies (59). |
| 3 September 1697 | North America [treaties] | The Treaty of Rijswijk ends King William's War in North America, restoring French and British colonial possessions to their pre-war status. |
| 3 September 1783 | UK, France, Spain, America, West Indies, Africa, India [treaties] | The Peace of Paris is signed between Britain on one side and France, Spain, and America on the other, ending the American Revolution. Britain recognizes the independence of the American colonies, cedes Florida to Spain, and recovers its West Indian possessions. France recovers St Lucia, Tobago, Senegal, Gorée, and its East Indian possessions. France regains the right to fortify Dunkirk. |
| 3 September 1866 | Prussia [administration] | Having defeated Austria and established Prussia as the leading power in Germany, the Prussian chancellor, Otto von Bismarck, obtains an indemnity from a grateful Prussian diet (state assembly) for having ruled without parliamentary approval of government budgets, ending the constitutional conflict that began in 1862. |
| 3 September 1878 | UK [transport disasters] | Over 600 people are killed in England when the pleasure steamer Princess Alice sinks in the Thames. |
| 3 September 1879 | Afghanistan, UK [wars] | Afghan troops massacre the British legation at Kabul, reigniting the Anglo-Afghan war ended by the Treaty of Gandamak on 26 May. |
| 3 September 1914 | [Catholicism] | Following the death of Pope Pius X on 20 August, the Italian clergyman Giacomo Della Chiesa is elected Pope Benedict XV. |
| 3 September 1930 | USA [railways] | US inventor Thomas Edison installs an experimental electric passenger train on the Lakawanna Railroad in New Jersey. |
| 3 September 1935 | USA [motor-racing and rallying] | British driver Malcolm Campbell drives Bluebird at 484.5 kph/301.1 mph at the Bonneville Salt Flats in Utah, USA; he sets a new land speed record. |
| 3 September 1939 | UK, France, Germany, Poland, Australia, New Zealand [World War II (1939–45)] | Britain and France declare war on Germany when it fails to respond to ultimatums following the German invasion of Poland. Australia and New Zealand also declare war on Germany. |
| 3 September 1939 | UK [everyday life] | The Citizens' Advice Bureaux scheme is launched in the UK with the opening of 200 offices. |
| 3 September 1940 | USA, UK, Newfoundland [World War II (1939–45)] | The USA sells 50 veteran destroyers to Britain for use by the Royal Navy in World War II in return for a 99-year rent-free lease of bases in Newfoundland and the Caribbean. |
| 3 September 1943 | Italy, Germany, USA, UK [World War II (1939–45)] | Allied (British and US) forces land in mainland Italy; an armistice is signed between the Allies and the Italian government of Marshal Pietro Badoglio, the successor to the deposed dictator Benito Mussolini, on the same day. |
| 3 September 1967 | Sweden [transport] | Sweden changes to driving on the right. |
| 3 September 1991 | Italy, USA [births and deaths] | Frank Capra, Italian-born US film director who directed It's a Wonderful Life and Mr Smith Goes to Washington, dies in La Quinta, California (94). |
