|Centuries:||7th century – 8th century – 9th century|
|Decades:||770s 780s 790s – 800s – 810s 820s 830s|
|Years:||797 798 799 – 800 – 801 802 803|
|800 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1553|
|Chinese calendar||己卯年 (Earth Rabbit)
3496 or 3436
— to —
庚辰年 (Metal Dragon)
3497 or 3437
|- Vikram Samvat||856–857|
|- Shaka Samvat||722–723|
|- Kali Yuga||3901–3902|
|Japanese calendar||Enryaku 19
|Minguo calendar||1112 before ROC
|Seleucid era||1111/1112 AG|
|Thai solar calendar||1342–1343|
|Wikimedia Commons has media related to 800.|
Year 800 (DCCC) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. It was around this time that the Anno Domini calendar era became the prevalent method in Europe for naming years, so from this time on, the years began to be known as 800 and onwards.
- December 25 – Charlemagne, king of the Franks, is crowned Holy Roman Emperor by pope Leo III as Charles I with the title "Emperor of the Franks and the Lombards". The coronation takes place during mass at the Basilica of St. Peter in Rome on Christmas Day. The Frankish Empire is formed in Western Europe which is not recognized by empress Irene at Constantinople. This triggers a series of disputes with the Byzantines around who is officially ruling the former Western Roman Empire.
- The Rus' Khaganate (modern Russia) is created by people who are called Rus' after 182 year dominance of the Khazars. This is the starting period of the rise of the Kievan Rus', and the later states of Belarus and Ukraine (approximate date).
- King Eardwulf of Northumbria has his men seize prince Ealhmund, son of the late king Alhred, and put him to death. He is buried at Derby in the St. Alkmund's Church and later revered as a saint (approximate date).
- The first settlers of the Hawaiian Islands arrive (approximate date).
- Retirement of archbishop Hygeberht of Lichfield. He is succeeded by Ealdwulf. King Coenwulf of Mercia is on better terms with the archiepiscopal of Canterbury than his predecessor, and unsuccessfully attempts to have the Mercian archiepiscopal see transferred to London (approximate date).
- Book of Kells is written and illuminated in a Columban monastery in the British Isles (approximate date).
- Nominoe, duke of Brittany (approximate date)
- Robert III, Frankish nobleman (d. 834)
- Valentine, pope of the Catholic Church (d. 827)
- Ailill mac Fergusa, king of South Brega (Ireland)
- Alkelda, Anglo-Saxon princess (approximate date)
- Beatus of Liébana, monk and theologian (approximate date)
- September 26 – Berowulf, bishop of Würzburg
- Ealhmund, prince of Northumbria (approximate date)
- Luitgard, Frankish queen and wife of Charlemagne
- June 3 – Staurakios, Byzantine chief minister
- Vatsraja, king of the Gurjara-Pratihara Dynasty