1021

Year 1021 (MXXI) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar.

Europe

 * November – Emperor Henry II conducts his fourth Italian military campaign. He crosses the Brenner Pass with a 60,000-strong army, and reaches Verona, where he receives Lombard levies. Henry proceeds to Mantua and then into Ravenna, to spend Christmas there.
 * The Taifa of Valencia, a Moorish kingdom in Al-Andalus (modern Spain), becomes independent from the Caliphate of Córdoba (approximate date).

Africa

 * 13 February – On one of his habitual night rides in the outskirts of Cairo, the Fatimid caliph al-Hakim bi-Amr Allah disappears, most likely assassinated by disaffected palace factions, apparently involving his sister, Sitt al-Mulk.
 * 26 March – On the feast of Eid al-Adha, the death of al-Hakim, kept secret for six weeks, is announced, along with the succession of his son, al-Zahir li-i'zaz Din Allah. On the same day, al-Hakim's designated heir, Abd al-Rahim ibn Ilyas, is arrested in Damascus and brought to Egypt.
 * The last evidence of indigenous Christian and non-Arabophone culture in Tripolitania (modern Libya) is seen.

Asia

 * Senekerim-Hovhannes Artsruni, king of Vaspurakan (Greater Armenia), surrenders his kingdom to the Byzantine Empire. In return, he receives Sebasteia and becomes governor of Cappadocia.
 * Battle of Shirimni, the Byzantine Empire under Basil II defeats  the Kingdom of Georgia under Giorgi I at Shirimni, at the Lake Palakazio, modern Lake Çıldır, Turkey
 * Hovhannes-Smbat III, King of the Armenian kingdom of Ani, is attacked by his younger brother Ashot IV, and loses much power to him, becoming concurrent king of outlying territories.
 * Emperor Rajendra Chola I extends his influence of the Chola Empire to the banks of the Ganges River (North India) and invades Bengal.
 * Sultan Mahmud of Ghazni appoints Malik Ayaz to the throne, making Lahore (modern Pakistan) the capital of the Ghaznavid Empire.
 * The Chinese capital city of Kaifeng has some half a million residents by this year. Including all those present in the nine designated suburbs, the population is over a million people.

North America

 * Vikings known to be occupying L'Anse aux Meadows on Newfoundland (island).

Births

 * December 8 – Wang Anshi, Chinese chancellor (d. 1086)
 * Eudokia Makrembolitissa, Byzantine empress (d. 1096)
 * Fujiwara no Kanshi, Japanese empress consort (d. 1102)
 * Wugunai, Chinese chieftain of the Wanyan tribe (d. 1074)

Deaths

 * February 13 – Al-Hakim bi-Amr Allah, Fatimid caliph (b. 985)
 * March 5 – Arnulf, French archbishop and illegitimate son of Lothair III
 * March 16 – Heribert, archbishop of Cologne (b. c. 970)
 * July 7 – Fujiwara no Akimitsu, Japanese bureaucrat (b. 944)
 * August 17 – Erkanbald, German abbot and archbishop
 * August 29 – Minamoto no Yorimitsu, Japanese nobleman (b. 948)
 * Fujiwara no Yoshikane, Japanese nobleman (b. 957)
 * Hamid al-Din al-Kirmani, Fatimid scholar and philosopher
 * Hamza ibn 'Ali ibn-Ahmad, founding leader of the Druze
 * Liu Mei, Chinese official and general (approximate date)
 * Mac Cú Ceanain, king of Uí Díarmata (Ireland)
 * Shams al-Dawla, Buyid emir of Hamadan (Iran)
 * Trilochanapala, king of the Kabul Shani dynasty