991 (CMXCI) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar.
|Centuries:||9th century – 10th century – 11th century|
|Decades:||960s 970s 980s – 990s – 1000s 1010s 1020s|
|Years:||988 989 990 – 991 – 992 993 994|
- Battle of Maldon: The Anglo-Saxons are beaten by Viking invaders led by Olaf Tryggvason, later Olaf I of Norway.
- Sweyn I of Denmark gets his throne back.
- Theophanu, empress, mother of Otto III (b. 956)
- Emperor En'yū, emperor of Japan (b. 959)