AD 999

By place and name

Europe

• King Bermudo II abdicates in favor of his 5-year-old son Alfonso V as ruler of León. Moorish invaders have forced Bermudo to recognize the suzerainty of their leader, Umayyad vizier and the de facto ruler Al-Mansur.
• 9 September - Battle of Svolder: A Norwegian fleet, commanded by Olaf Tryggvason, is defeated by the combined fleet of the Danish king Sweyn Forkbeard and his Swedish counterpart Olaf the Swede, resulting in Tryggvason's death, and the splitting up of Norway between Sweden and Denmark.

  Ireland

• December 30 - Battle of Glenmama: The combined forces of Munster and Meath under Brian Boru inflict a crushing defeat on the allied armies of Leinster and Dublin near Lyons Hill.

  Central Asia

• The Karakhanids invade from north of the Syr Darya River, ending the Samanid Empire. The Samanid domains are split between the Ghaznavid Dynasty and the Karakhanids.

  By topic

Religion

• February 18 - Pope Gregory V dies after a 3-year pontificate in which the Crescentii family forced him to flee Rome. He is succeeded by Sylvester II as the 139th pope of the Catholic Church.
• Bishop Aldhun consecrates a cathedral, at a site where the remains of St. Cuthbert had been moved to in AD 995 from Lindisfarne because of the danger of Viking raids.
• Sigmundur Brestisson, a Viking chieftain, introduces Christianity in the Faroe Islands.