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1703 (MDCCIII) was a common year starting on Monday (dominical letter G) of the Gregorian calendar and a common year starting on Friday (dominical letter C) of the Julian calendar, the 1703rd year of the Common Era (CE) and Anno Domini (AD) designations, the 703rd year of the 2nd millennium, the 3rd year of the 18th century, and the 4th year of the 1700s decade. As of the start of 1703, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923. In the Swedish calendar it was a common year starting on Thursday, one day ahead of the Julian and ten days behind the Gregorian calendar.
- January 14 – An earthquake hits Norcia, Italy.
- January 30 (December 14 of previous year in the Chinese calendar) – In Japan, the revenge of the Forty-seven Ronin occurs, assassinating daimyō Kira Yoshinaka, the enemy of their former lord Asano Naganori, at his own mansion as a vengeance. 46 of the 47 samurai commit seppuku, a ritual suicide on March 20 (February 4 in the Chinese calendar).
- February – Soldiers at Fort Louis de la Mobile celebrate Mardi Gras in Mobile, starting the tradition for Mobile, Alabama.
- February 3 – An earthquake hits the town of L'Aquila, Italy, killing 3000 and damaging many buildings.
- April 21 – The Company of Quenching of Fire (i.e., a fire brigade) is founded in Edinburgh, Scotland.
- May 26 – Portugal joins the Grand Alliance.
- May 27 (May 16 OS) – The city of Saint Petersburg is founded in Russia following Peter the Great's reconquest of Ingria from Sweden during the Great Northern War.
- June 15 – Hungarians rebel under Prince Francis II Rákóczi.
- June – The completed Icelandic census of 1703 is presented in the Althing, the first complete census of any country.
- July 29–July 31 – Daniel Defoe is placed in a pillory, then imprisoned for four months for the crime of seditious libel, after publishing his politically satirical pamphlet The Shortest Way with the Dissenters (1702) (his release is granted in mid-November).
- August 23 – Edirne event: Sultan Mustafa II of the Ottoman Empire is dethroned.
- September 12 – War of the Spanish Succession – Habsburg Archduke Charles is proclaimed King of Spain but never exercises full rule.
- October – A whirlwind blows down the tower of the Gan Takal in Gondar, capital of Ethiopia, killing 30.
- November 15 – The Kurucs defeated the Austrians and its allies (from Denmark, Hungary and the Serbs) near Zvolen (present day Slovakia)
- November 19 – The Man in the Iron Mask dies in the Bastille.
- November 24–December 2 – The Great Storm of 1703, an Atlantic hurricane, ravages southern England and the English Channel, killing nearly 8,000, mostly at sea.
- November 30 – Isaac Newton is elected president of the Royal Society in London, a position he will hold until his death in 1727.
- December 27 – Portugal and England sign the Methuen Treaty, which gives preference to Portuguese wines imported into England.
- December 28 – Ahmed III succeeds the deposed Mustafa II as Ottoman Emperor.
- February 5 – Gilbert Tennent, Irish-born religious leader (d. 1764)
- March 5 (N. S.) – Vasily Trediakovsky, Russian poet (d. 1768)
- March 23 – Cajsa Warg, Swedish cookbook author (d. 1769)
- May 14 – David Brearly, delegate to the U.S. Constitutional Convention (d. 1785)
- June 26 – Thomas Clap, first president of Yale University (d. 1767)
- June 28 – John Wesley, English founder of Methodism and anti-slavery activist (d. 1791)
- August 2 – Lorenzo Ricci, Italian Jesuit leader (d. 1775)
- September 29 – François Boucher, French painter (d. 1770)
- October 5 – Jonathan Edwards, American preacher (d. 1758)
- October 13 – Andrea Belli, Maltese architect and businessman (d. 1772)
- October 28 – Antoine Deparcieux, French mathematician (d. 1768)
- November 25 – Jean-François Séguier, French astronomer and botanist (d. 1784)
- November 26 – Theophilus Cibber, English actor and writer (d. 1758)
- December 2 – Ferdinand Konščak, Croatian explorer (d. 1759)
- date unknown – Jack Broughton, English bare-knuckle fighter who produced the earliest known rules of boxing (d. 1789)
- January 11 – Johann Georg Graevius, German classical scholar and critic (b. 1632)
- February 18 – Ilona Zrínyi, Hungarian heroine (b. 1643)
- March 3 – Robert Hooke, English scientist (b. 1635)
- March 31 – Johann Christoph Bach, German composer (b. 1642)
- April 20 – Lancelot Addison, English royal chaplain (b. 1632)
- May 16 – Charles Perrault, French author (b. 1628)
- May 26 – Samuel Pepys, English civil servant and diarist (b. 1633)
- June 14 – Jean Herauld Gourville, French adventurer (b. 1625)
- July 17 – Roemer Vlacq I, Dutch naval captain (b. 1637)
- September 22 – Vincenzo Viviani, Italian mathematician and scientist (b. 1622)
- September 25 – Archibald Campbell, 1st Duke of Argyll, Scottish privy councillor (b. 1658)
- September 29 – Charles de Saint-Évremond, French soldier (b. 1610)
- October 28 – John Wallis, English mathematician (b. 1616)
- November 19 – The Man in the Iron Mask (identity unknown)
- November 30 – Nicolas de Grigny, French organist and composer (b. 1672)
- December 28 – Mustafa II, Ottoman Sultan (b. 1664)
- date unknown – Phetracha, king of Ayutthaya (b. 1632)
- ^ Lessard, Rénald (1995). "L'Épidémie de variole de 1702-1703". Cap-aux-Diamants : La Revue d'histoire du Québec (pdf) (in French). 42: 51.