April 20

• April 20, 121
  Marcus Aurelius, 16th Roman emperor, is born
• April 20, 1139
  Second Lateran Council, the tenth ecumenical council, opened in Rome to declare clerical marriages invalid, regulate clerical dress, and punish attacks on clerics by excommunication
• April 20, 1632
  Nicolas Antoine, a French Christian Protestant theologian converted to Judiasm, is burned at the stake
• April 20, 1653
  Oliver Cromwell dissolved the English parliament
• April 20, 1657
  English Admiral Robert Blake fights his last battle when he destroyed the Spanish fleet in Santa Cruz de Tenerife Bay
• April 20, 1769
  Ottawa Chief Pontiac is murdered by an Indian in Cahokia
• April 20, 1770
  Captain Cook arrives in New South Wales, Australia starting his exploration and mapping of Australia
• April 20, 1777
  New York adopts new constitution, written by Gouverneur Morris, as an independent state
• April 20, 1804
  Jean-Jacques Dessalines, Haitian rebel leader, commands 1804 Haiti Massacre of the French at town of Cape Francois, during which the white Haitians were practically eradicated
• April 20, 1809
  Napoleon defeat Austria in the Battle of Abensberg, Bavaria
• April 20, 1832
  US Congress passes legislation making thermal springs at Hot Springs, Arkansas, the first nationally protected area in the USA
• April 20, 1871
  The Enforcement Act of 1871, also known as the Ku Klux Klan Act, allows the President to suspend writ of habeas corpus
• April 20, 1902
  Marie and Pierre Curie isolate from a ton of pitchblende one-tenth of a gram of radium chloride
• April 20, 1919
  Polish Army captures Vilno, Lithuania during Polish-Soviet War
• April 20, 1992
  Seville's six-month Universal Exhibition opens, called Seville Expo 1992, in the city of Seville, Spain
• April 20, 1999
  Two Littleton, Colorado teenagers, Eric Harris and Dylan Klebold, open fire on their Columbine High School teachers and classmates, killing 12 students and one teacher, and then themselves
• April 20, 2006
  Iran announces a uranium enrichment deal with Russia, involving a joint uranium enrichment firm on Russian soil; nine days later Iran announces that it will not move all activity to Russia, thus leading to a de-facto termination of the deal
• April 20, 2009
  Oracle announces it will acquire Sun Microsystems for more than US$7 billion