April 9

193 – The distinguished soldier Septimius Severus is proclaimed emperor by the army in Illyricum. 475 – Byzantine Emperor Basiliscus issues a circular letter (Enkyklikon) to the bishops of his empire, supporting the Monophysite christological position. 537 – Siege of Rome: The Byzantine general Belisarius receives his promised reinforcements, 1,600 cavalry, mostly of Hunnic or Slavic origin and expert bowmen. He starts, despite shortages, raids against the Gothic camps and Vitiges is forced into a stalemate. 1241 – Battle of Liegnitz: Mongol forces defeat the Polish and German armies. 1288 – Mongol invasions of Vietnam: Yuan forces are defeated by Trần forces in the Battle of Bach Dang in present-day northern Vietnam. 1388 – Despite being outnumbered 16:1, forces of the Old Swiss Confederacy are victorious over the Archduchy of Austria in the Battle of Näfels. 1454 – The Treaty of Lodi is signed, establishing a balance of power among northern Italian city-states for almost 50 years. 1609 – Eighty Years' War: Spain and the Dutch Republic sign the Treaty of Antwerp to initiate twelve years of truce. 1609 – Philip III of Spain issues the decree of the "Expulsion of the Moriscos". 1682 – Robert Cavelier de La Salle discovers the mouth of the Mississippi River, claims it for France and names it Louisiana. 1784 – The Treaty of Paris, ratified by the United States Congress on January 14, 1784, is ratified by King George III of the Kingdom of Great Britain, ending the American Revolutionary War. Copies of the ratified documents are exchanged on May 12, 1784. 1860 – On his phonautograph machine, Édouard-Léon Scott de Martinville makes the oldest known recording of an audible human voice. 1865 – American Civil War: Robert E. Lee surrenders the Army of Northern Virginia (26,765 troops) to Ulysses S. Grant at Appomattox Court House, Virginia, effectively ending the war. 1909 – The U.S. Congress passes the Payne–Aldrich Tariff Act. 1917 – World War I: The Battle of Arras: The battle begins with Canadian Corps executing a massive assault on Vimy Ridge.