1021 (The People's Chronology)
Córdoba's resident Berbers persuade the late Ali ibn Hammud's son Yahya al-Mutali to take the city from Ali's brother al-Qasim, who took power in 1018 (but see 1022).
A Byzantine army sent by Basil II invades Armenia (see 1022).
Egypt's sixth Fatimid caliph al-Hakim disappears under mysterious circumstances at age 36. The Druse (Druze) leader Hamzah ibn Ali goes into hiding once again (see 1017); he claims that al-Hakim, as imam (a divinely appointed spokesman for Islam), has merely taken leave in order to test the faith of his followers, and although Hamzah himself will soon die, and Egyptians will drive out most of the Druse, the cult will flourish in Syria, where Hamzah's teachings and those of the late Muhammad ibn Ismail ad-Darazi will serve as the ideological foundation for many peasant revolts (see politics, 1925).
Epidemics of St. Vitus's dance sweep Europe. The disease is a chorea whose victims invoke the name of a Christian child martyr of the 3rd century.