642: Arab forces under Amr ibn al-‘As conquer Alexandria

1683: Dutch scientist Antonie van Leeuwenhoek is the first to report the existence of bacteria

1787: US Constitution is signed by delegates at the Philadelphia Convention

1862: Battle of Antietam [Battle of Sharpsburg]: Bloodiest day in the American Civil War with 22,000 dead, wounded, or missing in the first major battle on Union soil

1916: World War I flying ace, the Red Baron of the German Luftstreitkräfte, wins his first aerial combat near Cambrai, France

1940: Adolf Hitler indefinitely postpones Operation Sealion, the planned German invasion of Great Britain

1978: Anwar Sadat, Menachem Begin, and Jimmy Carter sign the Camp David Accords, frameworks for peace in the Middle East and between Egypt and Israel

Source: Onthisday.com