March 21

630 – Emperor Heraclius of Byzantium returns the True Cross relic to Jerusalem from Constantinople.

1788 –  Le Grand incendie de La Nouvelle Orléans – The Great New Orleans Fire, destroys 856 of the 1,100 structures in the city (now the French Quarter) in less than 5 hours.

1871 – Journalist Henry Morton Stanley begins his trek across Africa to find the missionary and explorer, Dr. David Livingstone.

1925 – The Butler Act prohibits the teaching of human evolution in Tennessee.

1928 – As he held a commission in the U.S. Army Air Corps Reserve, Charles Lindbergh is awarded the Medal of Honor for the first solo trans-Atlantic flight the previous year.

1963 – Alcatraz Federal Penitentiary in California closes.

1965 – NASA launches Ranger 9, the last unmanned lunar space probe.

1970 – The first Earth Day proclamation is issued by Joseph Alioto, Mayor of San Francisco.

1980 – President Carter announces a U.S. boycott of the 1980 Summer Olympics in Moscow to protest the Soviet–Afghan War.

1989 – Transbrasil Flight 801, a Boeing 707, crashes near São Paulo/Guarulhos International Airport, killing the 3 crew aboard and 22 more people on the ground.

1999 – Bertrand Piccard and Brian Jones become the first to circumnavigate the Earth in a hot air balloon.

2006 – The social media site Twitter is founded.