830Centuries: 8th century - 9th century - 10th century
- Christian missionary Ansgar visits Birka, trade city of the Swedes.
- Earliest date of composition for the Historia Brittonum, attributed to Nennius, and known for its list of 12 battles of King Arthur.
- Egbert of Wessex defeats the Welsh.
- Al-Khwarizmi writes the Hisab 'al-jabr' w?al-muqabala, an important work on algebra.
- Borobodur is completed as a Buddhist monument, after about 50 years of work.