Year 665 (DCLXV) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. The denomination 665 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
|Ab urbe condita||1418|
|Balinese saka calendar||586–587|
|Chinese calendar||甲子年 (Wood Rat)|
3361 or 3301
— to —
乙丑年 (Wood Ox)
3362 or 3302
|- Vikram Samvat||721–722|
|- Shaka Samvat||586–587|
|- Kali Yuga||3765–3766|
|Minguo calendar||1247 before ROC|
|Seleucid era||976/977 AG|
|Thai solar calendar||1207–1208|
791 or 410 or −362
— to —
792 or 411 or −361
- Kubrat, ruler (khagan) of Great Bulgaria, dies after a 33-year reign. He is succeeded by his son Batbayan, who rules from Poltava (modern Ukraine) the lands north of the Black Sea and the Sea of Azov.
- Conflict erupts between King Sighere of Essex and his brother Sæbbi, as they struggle for overlordship between Mercia and Wessex.
- Muslim Conquest: An Arab army (40,000 men) advances through the desert and captures the Byzantine city of Barca (Libya).
- The city of Seongnam (South Korea) is renamed Hansanju (approximate date).
- Wu Zetian, the wife of the Chinese emperor, unofficially becomes an absolute ruler by eliminating her political rivals.
- Wilfrid, Anglo-Saxon abbot, refuses to be consecrated in Northumbria as bishop, and travels to Compiègne (France) to be consecrated by Agilbert, archbishop of Paris.
- Jaruman, bishop of Mercia, is dispatched with Christian missionaries to reconvert Saxon tribes, which have returned to paganism.
- According to the Annales Cambriae, the Anglo-Saxons convert to Christianity after the Second Battle of Badon.
- Sighere encourages his subjects to reject Christianity and return to their indigenous religion (approximate date).