On this day: 21 March

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.

Emperor Heraclius returns the True Cross, one of the holiest Christian relics, to Jerusalem.

Battle of Vincy between Charles Martel and Ragenfrid.

Annulment of the marriage of King Louis VII of France and Queen Eleanor of Aquitaine.

Emperor Antoku accedes to the throne of Japan.

A large fire destroyed 856 of the 1,100 structures in New Orleans.

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.

Code Napoléon is adopted as French civil law.

War of the Sixth Coalition: During their march on Paris, Coalition forces defeated Napoleon's French army on the final day of the Battle of Arcis-sur-Aube.

Greek War of Independence: Greek revolutionaries seize Kalavryta.

During his tour of the United States, the Marquis de Lafayette laid the cornerstone for the Nathanael Greene Monument in Savannah, Georgia.

The Baháʼí calendar, used in the Baháʼí Faith, began.

Alexander H. Stephens, Vice President of the Confederate States of America, gave an extemporaneous speech laying out the Confederacy's rationale for seceding from the United States.

Otto von Bismarck is appointed as the first Chancellor of the German Empire.

First World War: The German Army opened the Spring Offensive with Operation Michael, attempting to break through the Allied lines and to seize ports on the English Channel.

The Hungarian Soviet Republic is established becoming the first Communist government to be formed in Europe after the October Revolution in Russia.

The New Economic Policy is implemented by the Bolshevik Party in response to the economic failure as a result of war communism.

Syngman Rhee is removed from office after being impeached as the President of the Provisional Government of the Republic of Korea.

Ravel's opera L'enfant et les sortilèges, to a libretto by Colette, is premiered at the Opéra de Monte-Carlo.

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

Charles Lindbergh is presented with the Medal of Honor for the first solo trans-Atlantic flight.

The landmark Australian Eastern Mission led by John Latham departs on its three-month tour of East and South-East Asia.

Shah of Iran Reza Shah Pahlavi formally asks the international community to call Persia by its native name, Iran.

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.

The Los Angeles Rams signed Kenny Washington, making him the first African-American player in the National Football League since 1933.

The Moondog Coronation Ball, generally considered to be the first major rock and roll concert, took place at the Cleveland Arena in Cleveland, Ohio.

The Federal Bureau of Prisons closed Alcatraz Federal Penitentiary on Alcatraz Island (pictured) in San Francisco Bay, California.

Alcatraz Federal Penitentiary closes.

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.

Ranger program: NASA launches Ranger 9, the last in a series of uncrewed lunar space probes.

War of Attrition: The Battle of Karameh took place between the Israel Defense Forces and allied troops of the Palestine Liberation Organization and the Jordanian Armed Forces.

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

San Diego Comic-Con, the largest pop and culture festival in the world, hosts its inaugural event.

Cold War: American President Jimmy Carter announces a United States boycott of the 1980 Summer Olympics in Moscow to protest the Soviet–Afghan War.

Debi Thomas becomes the first African American to win the World Figure Skating Championships.

Namibia becomes independent after 75 years of South African rule.

The United Nations Framework Convention on Climate Change enters into force.

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

Pope John Paul II makes his first ever pontifical visit to Israel.

Jack Dorsey sent the first message on the social-media network Twitter.