September 23

38 – Drusilla, Caligula's sister who died in June, with whom the emperor is said to have an incestuous relationship, is deified. 1122 – Pope Callixtus II and Holy Roman Emperor Henry V agree to the Concordat of Worms to put an end to the Investiture Controversy. 1338 – The Battle of Arnemuiden, in which a French force defeats the English, is the first naval battle of the Hundred Years' War and the first naval battle in which gunpowder artillery is used. 1409 – The Battle of Kherlen is the second significant victory over Ming dynasty China by the Mongols since 1368. 1459 – The Battle of Blore Heath, the first major battle of the English Wars of the Roses, is won by the Yorkists. 1561 – King Philip II of Spain issues cedula, ordering a halt to colonizing efforts in Florida. 1779 – American Revolution: John Paul Jones, naval commander of the United States, on board the , wins the Battle of Flamborough Head. 1803 – Second Anglo-Maratha War: The Battle of Assaye is fought between the British East India Company and the Maratha Empire in India. 1821 – Tripolitsa, Greece, is captured by Greek rebels during the Greek War of Independence. 1846 – Astronomers Urbain Le Verrier, John Couch Adams and Johann Gottfried Galle collaborate on the discovery of Neptune. 1868 – The Grito de Lares occurs in Puerto Rico against Spanish rule. 1884 – On the night of 23-24 September, the steamship Arctique runs aground near Cape Virgenes leading to the discovery of nearby placer gold, beginning the Tierra del Fuego gold rush. 1899 – The American Asiatic Squadron destroys a Filipino battery at the Battle of Olongapo. 1905 – Norway and Sweden sign the Karlstad Treaty, peacefully dissolving the Union between the two countries. 1942 – World War II: The Matanikau action on Guadalcanal begins: U.S. Marines attack Japanese units along the Matanikau River. 1950 – Korean War: The Battle of Hill 282 is the first US friendly-fire incident on British military personnel since World War II. 1973 – Argentine general election: Juan Perón returns to power in Argentina.