|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|
|Bahá'í calendar||−1044 – −1043|
|English Regnal year||N/A|
|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|
|Igbo calendar||−200 – −199|
|Japanese calendar||Enryaku 19
|Minguo calendar||1112 before ROC
|Thai solar calendar||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 - Pope Leo III crowns Charlemagne Emperor of the Holy Roman Empire in Saint Peter's Basilica in Rome.
- The Carolingian Empire is formed in western Europe.
- In Russia the Rus' Khaganate is born after 182 year dominance of the Khazars.
- The first settlers of the Hawaiian Islands arrive (approximate date).
- Book of Kells written and illuminated in a Columban monastery in the British Isles (approximate date)