AD 999

999 in various
AG
Thai solar calendar	1541–1542
Tibetan calendar	阳土狗年; (male Earth-Dog); 1125 or 744 or −28; — to —; 阴土猪年; (female Earth-Pig); 1126 or 745 or −27

Millennium:	1st millennium
Centuries:	9th century; 10th century ; 11th century;
Decades:	970s; 980s; 990s ; 1000s; 1010s;
Years:	996; 997; 998; 999 ; 1000; 1001; 1002;

Year 999 (CMXCIX) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar.

Events

9 February
: The Mogi Ceremony of Fujiwara no Shoshi is held (she later becomes empress).
December: Empress Teishi gives birth to Prince Atsuyasu (who becomes the imperial heir), but on the next day, her rival, Fujiwara no Shoshi, is promoted to Consort.

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 (999 or 1000) – 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.

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

Bishop Aldhun consecrates a cathedral (later Durham 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.