1042

By place

Byzantine Empire

• April 19 - Emperor Michael V Kalaphates banishes his adoptive mother and co-ruler Zoë, for plotting to poison him, to the island of Principo. His announcement as sole emperor leads to a popular revolt.
• April 20 - Zoë is proclaimed as empress at an assembly in Hagia Sophia along with her sister Theodora as co-ruler. Michael V flees to the monastery of Stoudios but is arrested, blinded and castrated.
• Zoë recalls Synodianos, governor of the Catepanate of Italy, and replaces him with George Maniakes. All of Apulia is in the hands of the Lombard rebels.
• June 11 - Zoë marries, a Byzantine bureaucrat who ascends as co-emperor Constantine IX at Constantinople. Theodora agrees to surrender her co-emperorship.
• Summer - George Maniakes goes on a march through Apulia, plundering the towns that have declared for the Lombard rebels. Constantine IX recalls Maniakes to Constantinople.
• George Maniakes revolts against Constantine IX and is declared emperor by his troops. He captures Pardos who has landed with an army at Otranto to take over his command.
• Byzantine–Arab War: The Byzantines reconquer the fortress city of Edessa. Returning it to Christian hands, after 400 years of Islamic rule.
• Duklja secures its independence from the Byzantine Empire.

  Europe

• January 25 - Abbad I dies after a 19-year reign as independent ruler of the Taifa of Seville in Al-Andalus. He is succeeded by his son Abbad II.
• Casimir I, duke of Poland, succeeds in reuniting the realm which earns him the name "the Restorer". He signs a treaty with Bretislav I, duke of Bohemia, at Regensburg.
• June 8 - Magnus the Good becomes king of Denmark after the death of Harthacnut. Despite of a claim to the throne by Sweyn II, Magnus takes control of Denmark.
• Autumn - Norman mercenaries assemble at Matera and decide to elect William Iron Arm as count of Melfi and leader of the Normans in Southern Italy.
• Harald Hardrada, leader of the Varangian Guard in the Byzantine Empire, returns to Norway, possibly because of his involvement in Maniakes' revolt.
• Finnish–Novgorodian War: Grand Prince Vladimir Yaroslavich wages a campaign against the Tavastians.

  England

• June 8 - King Harthacnut collapses while attending a party. He dies without an heir, Edward the Confessor becomes king of England.

  Islamic world

• The Almoravids, led by Abdallah ibn Yasin, invade Morocco.