1800

1800 (MDCCC) was an exceptional common year starting on Wednesday in the Gregorian calendar and a leap year starting on Sunday in the Julian calendar. Because of a leap day in the Julian calendar, the Gregorian calendar moved ahead by 12 days. It was the last year of the 18th century.

• World population hits 1 billion.
• March 14 – Cardinal Barnaba Chiaramonti is elected pope as Pius VII.
• March 21 – Pius VII is ordained.
• April 24 – U.S. Library of Congress founded.
• May 5 – Great Britain passes the Act of Union to join Great Britain and Ireland into the United Kingdom of Great Britain and Ireland to take effect on 1 January 1801. The act is signed by King George III in August.
• May 15 – Napoleon Bonaparte crosses the Alps and invades Italy.
• June 14 – Battle of Marengo, Napoleon defeats the Austrian troops near Marengo, Italy.
• June 2 – First smallpox vaccination in North America, at Trinity, Newfoundland.
• June 27 – Pascha Jussuf Karamanli of Tripoli declares war on Sweden by having the flagpole on the consulate chopped down.
• September 5 – The island of Malta, that was occupied by the French, is conquered by British troops.
• November 1 – U.S. President John Adams becomes the first President of the United States to live in the Executive Mansion (later renamed the White House).
• November 17 – The U.S. Congress holds its first Washington, DC session.
• December 3 – Battle of Hohenlinden, the French army defeats the Austrian troops.
• December 24 – An assault on Napoleon Bonaparte fails in Paris.
• December 24 – Pierre Coudrin and Henriette Aymer de la Chevalerie found the Congregation of the Sacred Hearts of Jesus and Mary in Paris.
• Invention of the voltaic pile by Alessandro Volta: the first chemical battery
• The infrared radiation is discovered by Wilhelm Herschel.
• The Althing of Iceland, the world's oldest parliament, is abolished.

for more information, see Category:1800 births.

January 7 - Millard Fillmore, thirteenth President of the United States (d. 1874)==Deaths==

for more information, see Category:1800 deaths.

November 30 - Charles Adams, son of John Adams (b. 1770)