|Covid-19|May 23 – Battle of Dandanaqan: Seljuk Turks defeat the Ghaznavids.
June 17 – Harthacanute lands at Sandwich and reclaims the English throne.
August 15 – King Duncan I is killed in battle against his first cousin and rival Macbeth, who succeeds him as King of Scotland.
Weihenstephan Abbey (Kloster Weihenstephan, in German), founds the oldest brewery.
The Shalu Monastery is founded in Tibet.
Woodblock printing is invented in China (approximate date).
February 22 – Rashi, French rabbi and commentator (d. 1105)
King Ladislaus I of Hungary (d. 1095)
Ida of Lorraine, French noblewoman (d. 1113)
Alan Rufus, Breton leader in England during the Norman Conquest (approximate date) (d. 1093)
Sikelgaita, duchess of Apulia (d. 1090)
March 17 – Harold Harefoot, King of England
June 21 – Fulk III, Count of Anjou
August 14 – King Duncan I of Scotland (b. 1001)
October 1 – Alan III, Duke of Brittany (poisoned) (b. 997)
Hugh, Count of Suio
Masud, Ghaznavid emperor
Alhazen; Arab or Persian scientist and polymath
Year 1040 (MXL) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar. It is the 40th year of the 11th century and of the 2nd millennium, and is the first year of the 1040s decade.