January - March

January 6 - Ottoman troops clash with men of a Maronite leader Karam in St. Doumit in Lebanon: Ottomans 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 7 - Battle of Abtao: A Spanish naval squadron fought a combined Peruvian-Chilean fleet, at the island of Abtao in the Chiloé Archipelago of central Chile.

February 13 - The first daylight bank 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 - June

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 Ferdinand Cohen-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.

Battle of Callao: Peruvian defenders fight off the Spanish fleet.

May 11 - London bank Overend, Gurney and Company collapses precipitating a financial crisis.

May 16 - The U.S. Congress approves the minting of a nickel five cent coin (nickel), elimination of its predecessor the half dime would not be completed until 1873 because of pressure from silver mining interests (Walter Breen).

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 - September

July 1 - The first Constitution of Romania was issued.

July 3 - At the Battle of Königgratz, the Prussian army under King Wilhelm and Helmuth von Moltke defeats the Austrian army of Lajos 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 - The Great Tea Race of 1866 ends in London, narrowly won by the clipper ship Taeping.

September 22 - Paraguay successfully defends Curupaity against the Triple Alliance, scoring more than 5000 with just about 50 casualties.

October - December

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 Pierre-Gustave 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.

October 15 - The Great Fire of Quebec (1866) destroys 2500 houses.

December 21 - Fetterman's massacre - Sioux ambush and wipe out 79 cavalrymen under lieutenant colonel William J. Fetterman

Undated

Federalist revolts occur in Argentina.

In Sweden the Riksdag of the Estates is replaced by an elected two chamber assembly, the Riksdag.

Alfred Nobel invents dynamite in Germany.

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" occurs (see: Haeckel).

Allemannia, rowing club is founded.

January - June

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)

April 24 - Ishii Kikujiro, Japanese diplomat (d. 1945)

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 - December

July 6 - Charles Mangin, French general (d. 1925)

July 13 - La Goulue, French dancer (d. 1929)

July 28 - Beatrix Potter, English children's author (d. 1943)

August 12

Jacinto Benavente, Spanish writer, Nobel Prize laureate (d. 1954)

Tom Dowse, Irish baseball player who played in major league baseball in the 1890s (d. 1946)

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)

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)

''date unknown''

Ethna Carbery, Northern Irish poet (d. 1902)

William D. Upshaw, American politician and temperance movement leader (d. 1952)

: ''See also :Category: 1866 births.''

January - June

January 23 - Thomas Love Peacock, English satirist (b. 1785)

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 6 - William Whewell, English scientist, philosopher, and historian of science (b. 1794)

March 20 - Rikard Nordraak, Norwegian composer (b. 1842)

March 21 - Nadezhda Durova, First, female, Russian officer (b. 1783)

March 28 - Solomon Foot, American politician (b. 1802)

April 4 - William Dick, Founder of Edinburgh Veterinary College (b. 1793)

April 5 - Thomas Hodgkin, British physician (b. 1798)

May 13 - Nikolai Brashman, Russian mathematician of Czech origin (b.1796)

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 - December

July 20 - Bernhard Riemann, German mathematician (b. 1826)

August 6 - Christian Eric Fahlcrantz, Swedish writer (b. 1790)

August 20 - Maria De Mattias, Catholic saint (b. 1805)

October 13 - Celadon Leeds Daboll, American merchant and inventor (b. 1818)

November 11 - Agustin Jerónimo de Iturbide y Huarte, Prince Imperial of Mexico (b. 1807)

November 26 - Jean-Jacques Willmar, Luxembourg politician (b. 1792)

December 1 - George Everest, Welsh geodesist (b. 1790)