21 March Events

March 21 is the 80th day of the year (81st in leap years) in the Gregorian calendar. There are 285 days remaining until the end of the year. This date is slightly more likely to fall on a Monday, Wednesday or Saturday (58 in 400 years each) than on Thursday or Friday (57), and slightly less likely to occur on a Tuesday or Sunday (56).
In astrology, the day of the equinox is the first full day of the sign of Aries. It is also the traditional first day of the astrological year. In the 21st century, the equinox usually occurs on March 19 or 20, being on March 21 only in 2003 and 2007. The next year in which the equinox occurs on March 21 is 2102.
Events

537 – Siege of Rome: King Vitiges attempts to assault the northern and eastern city walls, but is repulsed at the Praenestine Gate, known as the Vivarium, by the defenders under the Byzantine generals Bessas and Peranius.
630 – Emperor Heraclius returns the True Cross, one of the holiest Christian relics, to Jerusalem.
717 – Battle of Vincy between Charles Martel and Ragenfrid.
1152 – Annulment of the marriage of King Louis VII of France and Queen Eleanor of Aquitaine.
1188 – Emperor Antoku accedes to the throne of Japan.
1556 – In Oxford, Archbishop of Canterbury Thomas Cranmer is burned at the stake.
1788 – A fire in New Orleans leaves most of the town in ruins.
1800 – With the church leadership driven out of Rome during an armed conflict, Pius VII is crowned Pope in Venice with a temporary papal tiara made of papier-mâché.
1801 – The Battle of Alexandria is fought between British and French forces near the ruins of Nicopolis in Egypt.
1804 – Code Napoléon is adopted as French civil law.
1814 – Napoleonic Wars: Austrian forces repel French troops in the Battle of Arcis-sur-Aube.
1844 – The Bahá'í calendar begins. This is the first day of the first year of the Bahá'í calendar. It is annually celebrated by members of the Bahá'í Faith as the Bahá'í New Year or Náw-Rúz.
1861 – Alexander Stephens gives the Cornerstone Speech.
1871 – Otto von Bismarck is appointed Chancellor of the German Empire.
1871 – Journalist Henry Morton Stanley begins his trek to find the missionary and explorer David Livingstone.
1913 – Over 360 are killed and 20,000 homes destroyed in the Great Dayton Flood in Dayton, Ohio.
1918 – World War I: The first phase of the German Spring Offensive, Operation Michael, begins.
1919 – The Hungarian Soviet Republic is established becoming the first Communist government to be formed in Europe after the October Revolution in Russia.
1921 – The New Economic Policy is implemented by the Bolshevik Party in response to the economic failure as a result of war communism.
1925 – The Butler Act prohibits the teaching of human evolution in Tennessee.
1925 – Syngman Rhee is removed from office after being impeached as the President of the Provisional Government of the Republic of Korea.
1928 – Charles Lindbergh is presented with the Medal of Honor for the first solo trans-Atlantic flight.
1935 – Shah of Iran Reza Shah Pahlavi formally asks the international community to call Persia by its native name, Iran.
1937 – Ponce massacre: Nineteen people in Ponce, Puerto Rico are gunned down by police acting on orders of the US-appointed Governor, Blanton C. Winship.
1943 – Wehrmacht officer Rudolf von Gersdorff plots to assassinate Adolf Hitler by using a suicide bomb, but the plan falls through; von Gersdorff is able to defuse the bomb in time and avoid suspicion.
1945 – World War II: British troops liberate Mandalay, Burma.
1945 – World War II: Operation Carthage: Royal Air Force planes bomb Gestapo headquarters in Copenhagen, Denmark. They also accidentally hit a school, killing 125 civilians.
1945 – World War II: Bulgaria and the Soviet Union successfully complete their defense of the north bank of the Drava River as the Battle of the Transdanubian Hills concludes.
1946 – The Los Angeles Rams sign Kenny Washington, making him the first African American player in the American football since 1933.
1952 – Alan Freed presents the Moondog Coronation Ball, the first rock and roll concert, in Cleveland, Ohio.
1960 – Apartheid: Sharpeville massacre, South Africa: Police open fire on a group of unarmed black South African demonstrators, killing 69 and wounding 180.
1963 – Alcatraz Federal Penitentiary (in California) closes.
1965 – Ranger program: NASA launches Ranger 9, the last in a series of unmanned lunar space probes.
1965 – Dr. Martin Luther King, Jr. leads 3,200 people on the start of the third and finally successful civil rights march from Selma to Montgomery, Alabama.
1968 – Battle of Karameh in Jordan between the Israel Defense Forces and the combined forces of the Jordanian Armed Forces and PLO.
1970 – The first Earth Day proclamation is issued by Joseph Alioto, Mayor of San Francisco.
1980 – US President Jimmy Carter announces a United States boycott of the 1980 Summer Olympics in Moscow to protest the Soviet war in Afghanistan.
1983 – The first cases of the 1983 West Bank fainting epidemic begin; Israelis and Palestinians accuse each other of poison gas, but the cause is later determined mostly to be psychosomatic.
1986 – Debi Thomas became the first African American to win the World Figure Skating Championships
1990 – Namibia becomes independent after 75 years of South African rule.
1994 – The United Nations Framework Convention on Climate Change enters into force.
1999 – Bertrand Piccard and Brian Jones become the first to circumnavigate the Earth in a hot air balloon.
2000 – Pope John Paul II makes his first ever pontifical visit to Israel.
2006 – The social media site Twitter is founded.
2009 – Four police officers are shot and killed and a fifth is wounded in two shootings at Oakland, California.
Holidays and observances

Arbor Day (Portugal)
Birth of Benito Juárez, a Fiestas Patrias (Mexico)
Christian feast day:
Benedetta Cambiagio Frassinello
Nicholas of Flüe
Serapion of Thmuis
Thomas Cranmer (Anglicanism)
March 21 (Eastern Orthodox liturgics)
Earliest day on which Holy Saturday can fall, while April 24 is the latest; celebrated on the Saturday before Easter (Christianity)
Harmony Day (Australia)
Human Rights Day (South Africa)
Independence Day, celebrates the independence of Namibia from South African mandate in 1990
International Colour Day (International)
International Day for the Elimination of Racial Discrimination (International)
International Day of Forests (International), by proclamation of the United Nations General Assembly
Mother's Day (most of the Arab world)
National Tree Planting Day (Lesotho)
Newroz (Kurdistan, Mesopotamia, Iran)
Truant's Day (Poland, Faroe Islands)
Vernal Equinox related observances (see March 20)
World Down Syndrome Day (International)
World Poetry Day (International)
World Puppetry Day (International)
Youth Day (Tunisia)

Source: Wikipedia