25 December

333 – Emperor Constantine the Great elevates his youngest son Constans to the rank of Caesar.
350 – Vetranio meets Constantius II at Naissus (Serbia) and is forced to abdicate his title (Caesar). Constantius allows him to live as a private citizen on a state pension.
496 – Clovis I, king of the Franks, is baptized into the Catholic faith at Rheims, by Saint Remigius.
800 – Coronation of Charlemagne as Holy Roman Emperor, in Rome.
1000 – The foundation of the Kingdom of Hungary: Hungary is established as a Christian kingdom by Stephen I of Hungary.
1066 – William the Conqueror is crowned king of England, at Westminster Abbey, London.
1100 – Baldwin of Boulogne is crowned the first King of Jerusalem in the Church of the Nativity.
1130 – Count Roger II of Sicily is crowned the first King of Sicily.
1261 – John IV Lascaris of the restored Eastern Roman Empire is deposed and blinded by orders of his co-ruler Michael VIII Palaeologus.
1553 – Battle of Tucapel: Mapuche rebels under Lautaro defeat the Spanish conquistadors and executes the governor of Chile, Pedro de Valdivia.
1643 – Christmas Island found and named by Captain William Mynors of the East India Company vessel, the Royal Mary.
1776 – George Washington and the Continental Army cross the Delaware River to attack the Kingdom of Great Britain's Hessian mercenaries in Trenton, New Jersey.
1826 – The Eggnog Riot at the United States Military Academy concludes after beginning the previous evening.
1837 – Battle of Lake Okeechobee.
1868 – U.S. President Andrew Johnson grants unconditional pardon to all Civil War Confederate soldiers.
1914 – World War I: Known as the Christmas truce, German and British troops on the Western Front temporarily cease fire.
1926 – Emperor Taishō of Japan dies. His son, Prince Hirohito succeeds him as Emperor Shōwa.
1927 – The Vietnamese Nationalist Party is founded.
1932 – A magnitude 7.6 earthquake in Gansu, China kills 275 people.
1941 – Admiral Chester W. Nimitz arrives at Pearl Harbor to assume command of the U.S. Pacific Fleet
1941 – World War II: Battle of Hong Kong ends, beginning the Japanese Occupation of Hong Kong.
1941 – Admiral Émile Muselier seizes the archipelago of Saint Pierre and Miquelon, which become the first part of France to be liberated by the Free French Forces.
1946 – The first in Europe artificial, self-sustaining nuclear chain reaction is initiated within Soviet nuclear reactor F-1.
1947 – The Constitution of the Republic of China goes into effect.
1950 – The Stone of Scone, traditional coronation stone of British monarchs, is taken from Westminster Abbey by Scottish nationalist students. It later turns up in Scotland on April 11, 1951.
1963 – Turkish Cypriot Bayrak Radio begins transmitting in Cyprus after Turkish Cypriots are forcibly excluded from Cyprus Broadcasting Corporation.
1965 – The Yemeni Nasserite Unionist People's Organisation is founded in Taiz
1968 – Apollo program: Apollo 8 performs the very first successful Trans Earth Injection (TEI) maneuver, sending the crew and spacecraft on a trajectory back to Earth from Lunar orbit.
1968 – 42 Dalits are burned alive in Kilavenmani village, Tamil Nadu, India, a retaliation for a campaign for higher wages by Dalit labourers.
1974 – Cyclone Tracy devastates Darwin, Northern Territory Australia.
1974 – Marshall Fields drives a vehicle through the gates of the White House, resulting in a four-hour standoff.
1977 – Prime Minister of Israel Menachem Begin meets in Egypt with President of Egypt Anwar Sadat.
1989 – Nicolae Ceauşescu, former communist President of Romania and his wife, First-Deputy Prime-Minister Elena are condemned to death and executed after a flawed and summary trial.
1990 – The first successful trial run of the system which would become the World Wide Web.
1991 – Mikhail Gorbachev resigns as president of the Soviet Union (the union itself is dissolved the next day). Ukraine's referendum is finalized and Ukraine officially leaves the Soviet Union.
2000 – Russian President Vladimir Putin signs a bill into law that officially establishes a new National Anthem of Russia, with music adopted from the anthem of the Soviet Union that was composed by Alexander Vasilyevich Alexandrov.
2003 – The ill-fated Beagle 2 probe, released from the Mars Express Spacecraft on December 19, disappears shortly before its scheduled landing.
2004 – Cassini orbiter releases Huygens probe which successfully landed on Saturn's moon Titan on January 14, 2005.
2009 – Umar Farouk Abdulmutallab unsuccessfully attempts a terrorist attack against the US while on board a flight to Detroit Metro Airport Northwest Airlines Flight 253

Holidays and observances

Christian Feast Day:
Anastasia of Sirmium (Catholic Church)
December 25 (Eastern Orthodox liturgics)
Christmas Day, Christian holiday commemorating the birth of Jesus Christ. (International)
Constitution Day (Republic of China)
Malkh-Festival (Nakh peoples of Chechenya and Ingushetia)
Quaid-e-Azam's Day (Pakistan)