|849 by topic|
|Ab urbe condita||1602|
|Balinese saka calendar||770–771|
|Chinese calendar||戊辰年 (Earth Dragon)
3545 or 3485
— to —
己巳年 (Earth Snake)
3546 or 3486
|- Vikram Samvat||905–906|
|- Shaka Samvat||770–771|
|- Kali Yuga||3949–3950|
|Japanese calendar||Kashō 2
|Minguo calendar||1063 before ROC
|Seleucid era||1160/1161 AG|
|Thai solar calendar||1391–1392|
975 or 594 or −178
— to —
976 or 595 or −177
|Wikimedia Commons has media related to 849.|
- Battle of Ostia: A Saracen Arab fleet from Sardinia sets sail towards Rome. In response, Pope Leo IV forms a coalition of maritime Italian cities, including Naples, Amalfi and Gaeta, led by Admiral Caesar — which is assembled off the re-fortified port of Ostia — and repels the Saracen marauders. Their navy is scattered, resulting in many sunken vessels. Rome is saved from plunder and the expansion of the Aghlabids.
- Frankish forces under King Charles the Bald invade southern France, and conquer the territory of Toulouse. He appoints Fredelo as count (comté) of Toulouse, who founds the Rouergue dynasty. Aquitaine is submitted to the West Frankish Kingdom.
- The Armenian prince Bagrat II begins a rebellion against Caliph Al-Mutawakkil, of the Abbasid Caliphate.
- In the Chinese capital city of Chang'an, an imperial prince is impeached during the Tang Dynasty from his position by officials at court, for erecting a building that obstructs a street in the northwesternmost ward in South Central Chang'an.
- King Pyinbya of Burma founds the city of Pagan, located in the Mandalay Region, and fortifies it with walls.
- Ali ibn al-Madini, Muslim scholar (b. 778)
- Conaing mac Flainn, king of Brega (Ireland)
- Connagan, bishop of Clonfert (Ireland)
- Guntbold, archbishop of Rouen
- Harthamah ibn al-Nadr, Muslim governor
- Itakh al-Khazari, Muslim general
- Ragenar, bishop of Amiens
- Theophylact, Byzantine co-emperor
- Walafrid Strabo, Frankish theological writer
- Zhang Zhongwu, Chinese general