1866 (MDCCCLXVI) is a common year starting on Monday of the Gregorian calendar or a common year starting on Wednesday of the 12-day-slower Julian calendar.

Events

January – June

• January 6 – Ottoman troops clash with men of a Maronite leader Karam in St. Doumit in Lebanon - Turks are defeated
• January 12 - Royal Aeronautical Society is formed (London)
• January 28 - 800 Maronite troops clash with Ottoman troops in Karem Saddah, modern-day Lebanon - more battles between nationalist Maronites and Ottoman army follow
• February 13 - The first daylight robbery in United States history during peacetime takes place in Liberty, Missouri. This is considered to be the first robbery committed by Jesse James and his gang, although James's role is disputed.
• February 26 - The Calaveras Skull is discovered. Purported to be evidence of humans during the Pliocene Age, it turns out to be a hoax.
• March 27- Andrew Rankin patents the urinal.
• April 4 - Alexander II of Russia narrowly escapes an assassination attempt in the city of Kiev. A design for a city gate to commemorate his escape was the inspiration for Mussorgsky's The Great Gate of Kiev from Pictures at an Exhibition.
• April 10 - The American Society for the Prevention of Cruelty to Animals (ASPCA) is founded in New York City by Henry Bergh.
• May - Student Choen Blind fails to assassinate Otto von Bismarck in Unter den Linden in Berlin
• May 2 Battle of Estero Bellaco. Paraguayan forces attack the vanguard of the Triple Alliance Army (Brazil, Argentina and Uruguay) War of the Triple Alliance.
• May 2 - Peruvian defenders fight off Spanish fleet at the Battle of Callao.
• May 11 - London bank Overend, Gurney and Company collapses precipitating a financial crisis.
• May 16 - The U.S. Congress eliminates the half dime coin and replaces it with the five cent piece, or nickel.
• May 16 - Charles Elmer Hires invents root beer.
• May 24 - Battle of Tuyutí - 32.000 soldiers of the Triple Alliance defeat 24.000 Paraguayan soldiers few miles north of the Paraná, Argentina - 16.000 casualties.
• June 2 - Fenian forces skirmish with Canadian militia at Ridgeway and Fort Erie
• June 5 - Calculations indicate Pluto reached its most recent aphelion (furthest point from Sun) on this day. The next aphelion will occur in August 2113.
• June 8 - The Canadian Parliament meets for the first time in Ottawa.
• June 11 - Agra High Court established (later shifted to Allahabad High Court.
• June 14 - Beginning of the Austro-Prussian War, when the Austrians and most of the medium German states declare war on Prussia.
• June 20 - The Kingdom of Italy declares war on Austria.
• June 24 - At the Second Battle of Custozza, the Austrian army under Archduke Albrecht defeats the main Italian army, commanded by King Victor Emmanuel.
• June 27-June 29 - The Prussians defeat the Hanoverian army at the Battle of Langensalza.

July – December

• July 3 - At the Battle of Königgratz, the Prussian army under King Wilhelm and Helmuth von Moltke defeats the Austrian army of Ludwig von Benedek, leading to a decisive Prussian victory in the Austro-Prussian War.
• July 5 - Marriage of Princess Helena of the United Kingdom, third daughter of Queen Victoria to Prince Christian of Schleswig-Holstein-Sonderburg-Augustenburg
• July 20 - At the Naval Battle of Lissa, the Austrian fleet under Wilhelm von Tegetthoff defeats the Italian fleet of Carlo di Persano.
• July 24 - Reconstruction: Tennessee becomes the first U.S. state to be readmitted to the Union following the American Civil War.
• July 25 - The U.S. Congress passes legislation authorizing the rank of General of the Army (now called "5-star general") Lieutenant General Ulysses S. Grant becomes the first to have this rank.
• July 27 - The Atlantic Cable is successfully completed, allowing transatlantic telegraph communication for the first time.
• July 28 - The Metric Act of 1866 becomes law and legalizes the standardization of weights and measures in the United States.
• August 23 - Treaty of Prague ends the Austro-Prussian War
• September 22 - Paraguay successfully defends Curupaity against the Triple Alliance, scoring more than 5000 with just about 50 casualties.
• October 12 - The Treaty of Vienna ends the war between Austria and Italy. It formalizes the annexation of Venetia by Italy.
• October 14 - French troops under the command of Rear Admiral Gustav Roze land at Ganghwa Island, Korea as part of a punitive expedition against that kingdom for the execution of French Jesuit priests. It is the first military contact between Korea and a Western force.
• December 21 - Fetterman's massacre - Sioux ambush and wipe out 79 cavalrymen under lieutenant colonel William J. Fetterman

• Federalist revolts in Argentina
• In Sweden the Riksdag of the Estates is replaced by an elected two chamber assembly, the Riksdag.
• Alfred Nobel invents dynamite.
• First historical mention of gerbils, "yellow rats" sent to Museum of Natural History (Musée d'Histoire Naturelle) in Paris, by father Armand David from northern China
• First use of the term Ecology

Births

• January 13 - Vasily Kalinnikov, Russian composer (d. 1901)
• January 15 - Nathan Söderblom, Swedish archbishop, recipient of the Nobel Peace Prize (d. 1931)
• January 29 - Romain Rolland, French writer, Nobel Prize laureate (d. 1944)
• March 30 - George Van Haltren, baseball player (d. 1945)
• April 1 - Ferruccio Busoni, Italian pianist and composer (d. 1924)
• April 13 - Butch Cassidy, American outlaw (d. 1909)
• April 17 - Ernest Starling, British physiologist (d. 1927)
• May 5 - Thomas B. Thrige, Danish industrialist (d. 1938)
• May 17 - Erik Satie, French composer (d. 1925)
• June 4 - Miina Sillanpää, Finnish politician (d. 1952)
• June 26 - George Herbert, 5th Earl of Carnarvon, English financier of Egyptian excavations (d. 1923)
• July 28 - Beatrix Potter, English children's author (d. 1943)
• August 12 - Jacinto Benavente, Spanish writer, Nobel Prize laureate (d. 1954)
• September 1 - James J. Corbett, American boxer (d. 1933)
• September 7 - Tristan Bernard, French writer (d. 1947)
• September 10 - Jeppe Aakjaer, Danish poet and novelist (d. 1930)
• September 21 - Charles Nicolle, French bacteriologist, recipient of the Nobel Prize in Physiology or Medicine (d. 1936)
• September 21 - H. G. Wells, English writer (d. 1946)
• September 27 - Eurosia Fabris, Italian Catholic Blessed (d. 1932)
• September 25 - Thomas Hunt Morgan, American geneticist, recipient of the Nobel Prize in Physiology or Medicine (d. 1945)
• October 12 - Ramsay MacDonald, Prime Minister of the United Kingdom (d. 1937)
• November 12 - Sun Yat-sen, Chinese revolutionary (d. 1925)
• November 30 - Robert Broom, Scottish paleontologist (d. 1951)
• December 12 - Alfred Werner, German chemist, Nobel Prize laureate (d. 1919)
• December 16 (December 4 O.S.) - Wassily Kandinsky, Russian-born painter (d. 1944)

Unknown date

• Ethna Carbery, Northern Irish poet (d. 1902)
• Charles Mangin, French general (d. 1925)
• La Goulue, French dancer (d. 1929)
• Kikujiro Ishii, Japanese diplomat (d. 1945)
• William D. Upshaw, American politician and temperance movement leader (d. 1952)

Deaths

• January 31 - Friedrich Rückert, German poet, translator, and professor of Oriental languages (b. 1788)
• January - Thomas Baldwin Marsh, American religious leader (b. 1799)
• March 4 - Alexander Campbell, Irish/US founder of the Disciples of Christ (b. 1788)
• March 20 - Rikard Nordraak, Norwegian composer (b. 1842)
• May 29 - Winfield Scott, American general and presidential candidate (b. 1786)
• June 7 - Chief Sealth, Native American whom Seattle is named for (b. circa 1786)
• July 20 - Bernhard Riemann, German mathematician (b. 1826)
• November 26 - Jean-Jacques Willmar, Luxembourg politician (b. 1792)

1866

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