1303 – The Sapienza University of Rome is instituted by Pope Boniface VIII.
1453 – The last naval battle in Byzantine history occurs, as three Genoese galleys escorting a Byzantine transport fight their way through the huge Ottoman blockade fleet and into the Golden Horn.
1534 – Jacques Cartier begins the voyage during which he discovers Canada and Labrador.
1535 – The Sun dog phenomenon observed over Stockholm and depicted in the famous painting Vädersolstavlan.
1653 – Oliver Cromwell dissolves the Rump Parliament.
1657 – Admiral Robert Blake destroys a Spanish silver fleet under heavy fire at the Battle of Santa Cruz de Tenerife.
1657 – Freedom of religion is granted to the Jews of New Amsterdam (later New York City).
1689 – The former king, James II of England, now deposed, lays siege to Derry.
1752 – Start of Konbaung–Hanthawaddy War, a new phase in the Burmese Civil War (1740–57).
1770 – The Georgian king, Erekle II, abandoned by his Russian ally Count Totleben, wins a victory over Ottoman forces at Aspindza.
1775 – American Revolutionary War: The Siege of Boston begins, following the battles at Lexington and Concord.
1789 – President George Washington arrives in Philadelphia after his inauguration to elaborate welcome at Gray's Ferry just after noon first inauguration of George Washington
1792 – France declares war against the "King of Hungary and Bohemia", the beginning of French Revolutionary Wars.
1800 – The Septinsular Republic is established.
1809 – Two Austrian army corps in Bavaria are defeated by a First French Empire army led by Napoleon I of France at the Battle of Abensberg on the second day of a four-day campaign that ended in a French victory.
1810 – The Governor of Caracas declares independence from Spain.
1818 – The case of Ashford v Thornton ends, with Abraham Thornton allowed to go free rather than face a retrial for murder, after his demand for trial by battle is upheld.
1828 – René Caillié becomes the first non-Muslim to enter Timbouctou.
1836 – U.S. Congress passes an act creating the Wisconsin Territory.
1861 – American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.
1862 – Louis Pasteur and Claude Bernard complete the experiment falsifying the theory of spontaneous generation.
1865 – Astronomer Pietro Angelo Secchi demonstrates the Secchi disk, which measures water clarity, aboard Pope Pius IX's yacht, the L'Immaculata Concezion.
1871 – The Civil Rights Act of 1871 becomes law.
1876 – The April Uprising, a key point in modern Bulgarian history, leading to the Russo-Turkish War and the liberation of Bulgaria from domination as an independent part of the Ottoman Empire.
1884 – Pope Leo XIII publishes the encyclical Humanum genus.
1902 – Pierre and Marie Curie refine radium chloride.
1908 – Opening day of competition in the New South Wales Rugby League.
1912 – Opening day for baseball's Tiger Stadium in Detroit, Michigan, and Fenway Park in Boston.
1914 – Nineteen men, women, and children die in the Ludlow Massacre during a Colorado coal-miner's strike.
1916 – The Chicago Cubs play their first game at Weeghman Park (currently Wrigley Field), defeating the Cincinnati Reds 7–6 in 11 innings.
1918 – Manfred von Richthofen, a.k.a. The Red Baron, shoots down his 79th and 80th victims, his final victories before his death the following day.
1922 – The Soviet government creates South Ossetian Autonomous Oblast within Georgian SSR.
1926 – Western Electric and Warner Bros. announce Vitaphone, a process to add sound to film.
1939 – Adolf Hitler's 50th birthday is celebrated as a national holiday in Nazi Germany.
1939 – Billie Holiday records the first civil rights song "Strange Fruit".
1945 – World War II: US troops capture Leipzig, Germany, only to later cede the city to the Soviet Union.
1945 – World War II: Führerbunker: Adolf Hitler makes his last trip to the surface to award Iron Crosses to boy soldiers of the Hitler Youth.
1945 – Twenty Jewish children used in medical experiments at Neuengamme are killed in the basement of the Bullenhuser Damm school.
1946 – The League of Nations officially dissolves, giving most of its power to the United Nations.
1951 – Dan Gavriliu performs the first surgical replacement of a human organ.
1961 – Failure of the Bay of Pigs Invasion of US-backed Cuban exiles against Cuba.
1964 – BBC Two launches with a power cut because of the fire at Battersea Power Station.
1968 – English politician Enoch Powell makes his controversial Rivers of Blood speech.
1972 – Apollo 16, commanded by John Young, lands on the moon.
1978 – Korean Air Lines Flight 902 is shot down by the Soviet Union.
1980 – Climax of Berber Spring in Algeria as hundreds of Berber political activists are arrested.
1984 – The Good Friday Massacre, an extremely violent ice hockey playoff game, is played in Montreal, Canada.
1985 – The ATF raids The Covenant, The Sword, and the Arm of the Lord compound in northern Arkansas.
1986 – Pianist Vladimir Horowitz performs in his native Russia for the first time in 61 years.
1998 – German terrorist group the Red Army Faction announces their dissolution after 28 years.
1999 – Columbine High School massacre: Eric Harris and Dylan Klebold killed 13 people and injured 21 others before committing suicide at Columbine High School in Columbine, Colorado.
2007 – Johnson Space Center shooting: William Phillips with a handgun barricades himself in NASA's Johnson Space Center in Houston, Texas before killing a male hostage and himself.
2008 – Danica Patrick wins the Indy Japan 300 becoming the first female driver in history to win an Indy car race.
2010 – The Deepwater Horizon drilling rig explodes in the Gulf of Mexico, killing eleven workers and beginning an oil spill that would last six months.
2012 – One hundred twenty-seven people are killed when a plane crashes in a residential area near the Benazir Bhutto International Airport near Islamabad, Pakistan.
2013 – A 6.6-magnitude earthquake strikes Lushan County, Ya'an, in China's Sichuan province, killing more than 150 people and injuring thousands.