July 18 is the 199th day (200th in leap years) of the year in the Gregorian Calendar, with 166 days remaining.
- 390 BC - Battle of the Allia: A Roman army is defeated by raiding Gauls, leading to the subsequent sacking of Rome.
- 64 - Great fire of Rome: A fire begins to burn in the merchant area of Rome and soon burns completely out of control while Emperor Nero reportedly plays his lyre and sings while watching the blaze from a safe distance.
- 1830 - Uruguay adopts its first constitution.
- 1863 - American Civil War: The first formal African American military unit, the 54th Massachusetts Volunteer Infantry, unsuccessfully assaults Confederate-held Fort Wagner but their valiant fighting still proves the worth of African American soldiers during the war.
- 1873 - Oscar II of Sweden-Norway is crowned king of Norway in Trondheim
- 1898 - Marie Curie and Pierre Curie announced the discovery of a new element and proposed to call it polonium.
- 1914 - Within the United States Army the Signal Corps is formed giving definite status to its air service for the first time.
- 1925 - Adolf Hitler publishes his personal manifesto Mein Kampf.
- 1942 - World War II: The Germans test fly the Messerschmitt Me-262 using only its jets for the first time.
- 1944 - World War II: Hideki Tojo resigns as Prime Minister of Japan due to numerous setbacks in the war effort.
- 1947 - President Harry S. Truman signs the Presidential Succession Act into law which places the Speaker of the House and the Senate President Pro Tempore next in the line of succession after the United States Vice President.
- 1968 - Vietnam War: The two-day Honolulu Conference begins in Honolulu, Hawaii between US President Lyndon B. Johnson and South Vietnamese President Nguyen Van Thieu.
- 1968 - Intel incorporated.
- 1969 - After a party on Chappaquiddick Island, Senator Edward Kennedy from Massachusetts drives an Oldsmobile off a wooden bridge into a tide-swept pond and his passenger, Mary Jo Kopechne, drowns. Kennedy doesn't report the incident for 10 hours.
- 1969 - Apollo 11 makes preparations for landing on the Moon.
- 1976 - Gymnast Nadia Comaneci, aged 14, scores first ever perfect 10 at Olympics.
- 1984 - In San Ysidro, California, 41-year-old James Oliver Huberty sprays a McDonald's restaurant with gun-fire killing 21 people before being shot dead by police.
- 1986 - A tornado is broadcast live on KARE television in Minnesota when the station's helicopter pilot makes a chance encounter.
- 1986 - Aliens opens in theaters.
- 1994 - In Buenos Aires, an explosion destroys a building housing several Jewish organizations killing 96 and injuring many more.
- 1995 - On the Caribbean island of Montserrat, the Soufriere Hills volcano erupts. Over the course of several years, it devastates the island, destroying the capital and forcing most of the population to flee.
- 1996 - Storms provoke severe flooding on the Saguenay River in Quebec, beginning one of Canada's costliest natural disasters ever.
- 1996 - In an event very similar to the Oklahoma tornado that would occur 3 years later, a tornado ranking as a F5 hit the town of Oakfield, Wisconsin.
- 2001 - In Baltimore, Maryland, a 60-car train derailment occurs in a tunnel sparking a fire that will last days and virtually shut down downtown Baltimore.
- 1635 - Robert Hooke, scientist (d. 1703)
- 1811 - William Makepeace Thackeray, author (d. 1863)
- 1821 - Pauline Garcia-Viardot, singer/composer (d. 1910)
- 1853 - Hendrik Lorentz, Dutch physicist and Nobel laureate (d. 1928)
- 1863 - Franz Ferdinand, Archduke of Austria (d. 1914)
- 1864 - Ricarda Huch, writer (d. 1947)
- 1864 - Phillip Snowden, British politician (d. 1937)
- 1887 - Vidkun Quisling, Norwegian politician and famous traitor (d. 1945)
- 1890 - Frank Forde, fifteenth Prime Minister of Australia (d. 1983)
- 1902 - Nathalie Sarraute, writer (d. 1999)
- 1902 - Jessamyn West, writer (d. 1984)
- 1902 - Chill Wills, actor (d. 1978)
- 1906 - Clifford Odets, author, playwright (d. 1963)
- 1906 - S. I. Hayakawa, semanticist and politician (d. 1992)
- 1909 - Andrei Gromyko, Soviet diplomat and President 1985-1989 (d. 1989)
- 1909 - Mohammed Daoud Khan, Afghani President (1973-1978) (d. 1978)
- 1911 - Hume Cronyn, actor (d. 2003)
- 1913 - Red Skelton, actor, comedian (d. 1997)
- 1918 - Nelson Mandela, South Africa revolutionary and president
- 1921 - John Glenn, American astronaut and politician
- 1922 - Thomas Kuhn, philosopher (d. 1996)
- 1925 - Shirley Strickland, Australian athlete
- 1927 - Ludwig Harig, writer
- 1929 - Dick Button, Olympic gold medal figure skater
- 1929 - Screamin' Jay Hawkins (d. 2000)
- 1933 - Yevgeny Yevtushenko, poet
- 1937 - Roald Hoffman, Nobel prize-winning theoretical chemist
- 1937 - Hunter S. Thompson, journalist and author
- 1940 - James Brolin, actor
- 1940 - Joe Torre, baseball player, manager, New York Yankees
- 1941 - Martha Reeves, singer
- 1947 - Steve Forbes, entrepreneur, politician
- 1950 - Sir Richard Branson, entrepreneur
- 1963 - Martín Torrijos Espino, Panamanian president-elect
- 1963 - Mike Greenwell, baseball player
- 1967 - Vin Diesel, American actor, writer, and director
- 1975 - Torii Hunter, baseball player
- 1975 - Daron Malakian, guitarist for System of a Down
- 1374 - Petrarch, Italian Humanist
- 1623 - Pope Gregory XV
- 1721 - Antoine Watteau, French painter
- 1792 - John Paul Jones, American naval commander
- 1817 - Jane Austen, novelist
- 1949 - Vitezslav Novák, composer
- 1988 - Nico (Christa Paffgen), German and American model and singer
- 1990 - Yoon Boseon, President of South Korea
- 2001 - Fabio Taglioni, automotive engineer
- 2003 - Jane Barbe, voice of the telephone operator recording
- 2004 - Paul Foot, a British radical investigative journalist
Holidays and observances
July 17 - July 19 - June 18 - August 18 -- listing of all days
ca:18 de juliol
es:18 de julio
eo:18-a de julio
oc:18 de julhet
pt:18 de Julho