March 20 is the 79th day of the year (80th in leap years) in the Gregorian calendar. There are 286 days remaining until the end of the year. Typically the March equinox falls on this date, marking the vernal point in the Northern Hemisphere and the autumnal point in the Southern Hemisphere.
- 235 – Maximinus Thrax is proclaimed emperor.
- 673 – Emperor Tenmu of Japan assumes the Chrysanthemum Throne at the Palace of Kiyomihara in Asuka.
- 1206 – Michael IV Autoreianos is appointed Ecumenical Patriarch of Constantinople.
- 1600 – The Linköping Bloodbath takes place on Maundy Thursday in Linköping, Sweden: five Swedish noblemen are publicly beheaded in the aftermath of the War against Sigismund (1598–1599).[1]
- 1602 – The Dutch East India Company is established.
- 1616 – Sir Walter Raleigh is freed from the Tower of London after 13 years of imprisonment.
- 1760 – The Great Boston Fire of 1760 destroys 349 buildings.
- 1815 – After escaping from Elba, Napoleon enters Paris with a regular army of 140,000 and a volunteer force of around 200,000, beginning his "Hundred Days" rule.
- 1848 – German revolutions of 1848–49: King Ludwig I of Bavaria abdicates.
- 1852 – Harriet Beecher Stowe's Uncle Tom's Cabin is published.
- 1854 – The Republican Party of the United States is organized in Ripon, Wisconsin.
- 1861 – An earthquake destroys Mendoza, Argentina.
- 1883 – The Paris Convention for the Protection of Industrial Property is signed.
- 1888 – The premiere of the very first Romani language operetta is staged in Moscow, Russia.
- 1890 – Prime minister of the German Empire Otto von Bismarck is dismissed by Emperor Wilhelm II.
- 1896 – With the approval of Emperor Guangxu, the Qing dynasty post office is opened, marking the beginning of a postal service in China.
- 1913 – Sung Chiao-jen, a founder of the Chinese Nationalist Party, is wounded in an assassination attempt and dies 2 days later.
- 1915 – Albert Einstein publishes his general theory of relativity.
- 1921 – The Upper Silesia plebiscite was a plebiscite mandated by the Versailles Treaty to determine a section of the border between Weimar Germany and Poland.
- 1922 – The USS Langley is commissioned as the first United States Navy aircraft carrier.
- 1923 – The Arts Club of Chicago hosts the opening of Pablo Picasso's first United States showing, entitled Original Drawings by Pablo Picasso, becoming an early proponent of modern art in the United States.
- 1933 – Reichsführer-SS Heinrich Himmler ordered the creation of Dachau concentration camp as Chief of Police of Munich and appointed Theodor Eicke as the camp commandant.
- 1942 – World War II: General Douglas MacArthur, at Terowie, South Australia, makes his famous speech regarding the fall of the Philippines, in which he says: "I came out of Bataan and I shall return".
- 1948 – With a Musicians Union ban lifted, the first telecasts of classical music in the United States, under Eugene Ormandy and Arturo Toscanini, are given on CBS and NBC.
- 1951 – Fujiyoshida, a city located in Yamanashi Prefecture, Japan, in the center of the Japanese main island of Honshū is founded.
- 1952 – The US Senate ratifies the Security Treaty Between the United States and Japan.
- 1956 – Tunisia gains independence from France.
- 1964 – The precursor of the European Space Agency, ESRO (European Space Research Organisation) is established per an agreement signed on June 14, 1962.
- 1972 – The Troubles: The first Provisional IRA car bombing in Belfast kills seven people and injures 148 others in Northern Ireland.
- 1985 – Libby Riddles becomes the first woman to win the 1,135-mile Iditarod Trail Sled Dog Race.
- 1985 – Canadian paraplegic athlete and humanitarian Rick Hansen begins his circumnavigation of the globe in a wheelchair in the name of spinal cord injury medical research.
- 1987 – The Food and Drug Administration approves the anti-AIDS drug, AZT.
- 1988 – Eritrean War of Independence: Having defeated the Nadew Command, the Eritrean People's Liberation Front enters the town of Afabet, victoriously concluding the Battle of Afabet.
- 1990 – Ferdinand Marcos's widow, Imelda Marcos, goes on trial for bribery, embezzlement, and racketeering.
- 1993 – The Troubles: A Provisional IRA bomb kills two children in Warrington, England. It leads to mass protests in both Britain and Ireland.
- 1995 – The Japanese cult Aum Shinrikyo carries out a sarin gas attack on the Tokyo subway, killing 13 and wounding over 6,200 people.
- 1999 – Legoland California, the first Legoland outside of Europe, opens in Carlsbad, California.
- 2000 – Jamil Abdullah Al-Amin, a former Black Panther once known as H. Rap Brown, is captured after murdering Georgia sheriff's deputy Ricky Kinchen and critically wounding Deputy Aldranon English.
- 2003 – Invasion of Iraq: In the early hours of the morning, the United States and three other countries (the UK, Australia and Poland) begin military operations in Iraq.
- 2006 – Over 150 Chadian soldiers are killed in eastern Chad by members of the rebel UFDC. The rebel movement sought to overthrow Chadian president Idriss Déby.
- 2012 – At least 52 people are killed and more than 250 injured in a wave of terror attacks across ten cities in Iraq.
- 2014 – Four suspected Taliban members attack the luxurious Kabul Serena Hotel, killing at least nine people.
- 2015 – A Solar eclipse, equinox, and a Supermoon all occur on the same day.
