From Infogalactic: the planetary knowledge core
|Centuries:||8th century – 9th century – 10th century|
|Decades:||820s 830s 840s – 850s – 860s 870s 880s|
|Years:||848 849 850 – 851 – 852 853 854|
|851 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1604|
|Chinese calendar||庚午年 (Metal Horse)
3547 or 3487
— to —
辛未年 (Metal Goat)
3548 or 3488
|- Vikram Samvat||907–908|
|- Shaka Samvat||773–774|
|- Kali Yuga||3952–3953|
|Japanese calendar||Kashō 4 / Ninju 1
|Minguo calendar||1061 before ROC
|Seleucid era||1162/1163 AG|
|Thai solar calendar||1393–1394|
- Vikings plunder London and Canterbury.
- Charles the Bald, Louis the German and Lothar meet in Meersen.
- Garcia Iñiguez succeeds his father Iñigo Arista as king of Navarra.
- August 22 – Battle of Jengland. Erispoe, king of Brittany and son of Nominoe, defeats the Franc king Charles the Bald in Jengland-Beslé near Grand-Fougeray in Brittany. This is considered as the birth of the Breton state.
- September – Treaty of Angers. Charles the Bald acknowledges Erispoë as king of Brittany. He lets him have the County of Nantes, the County of Rennes and the County of Retz which become part of the Breton nation. The King of Brittany takes the oath to the King of France (but not an hommage lige which would be an allegiance). To mark the sovereignty of the Breton state, the Dukes of Brittany are since then crowned as "Duke, king in their lands".
- Oldest known mention of the Andaman Islands.
- Bagrat II Bagratuni, "Prince of Princes" of Arminiya, is captured by the Abbasid Caliphate and taken to Samarra.
- The Arab merchant Suleiman al-Tajir visits Tang Dynasty China, observing the manufacturing of Chinese porcelain at Guangzhou and writes of his admiration for its transparent quality. He also describes the mosque at Guangzhou, its granaries, its local government administration, some of its written records, and the treatment of travellers, along with the use of ceramics, rice-wine, and tea.