|Covid-19|Emperors Nikephoros I and Charlemagne settle their imperial boundaries in the Adriatic Sea, and sign the Pax Nicephori ("Peace of Nikephoros"). The Byzantines retain control of the coastal cities and islands in Dalmatian Croatia, while Frankish rule is accepted over Istria and the Dalmatian hinterland. Venice is recognized as independent by the Byzantine Empire.
Summer – Bardanes Tourkos, Byzantine general (strategos), is proclaimed emperor by the troops of the Anatolic, Opsikion, Thracian and Bucellarian themes. The 'rebel' army marches to Chrysopolis, a suburb of Constantinople. After the defection of two of his trusted aids, future emperors Leo the Armenian and Michael the Amorian, Bardanes negotiates peace.
May – Krum, ruler (khan) of the Bulgarian Empire, begins his territorial expansion and raids the Byzantine northern frontier. He leads his warriors — mostly Bulgars, Slavs, Thracians and Hellenized Macedonians — across the Carpathian Mountains, over the Danube River, and throughout Transylvania, Thrace, and Macedonia.
Stiftskeller St. Peter, possibly Central Europe's oldest restaurant, is founded in Salzburg, Austria.
Downfall of the Barmakids: Caliph Harun al-Rashid has his friend Ja'far ibn Yahya beheaded, possibly for having an affair with his sister Abassa. Surviving members of the influential Barmakid family are imprisoned on orders of Harun, and their property is confiscated.
October 12 – The Synod of Clofesho (possibly Brixworth) is held, at which the Archbishopric of Lichfield is demoted to an ordinary bishopric, with papal permission obtained by King Coenwulf of Mercia.
Du Mu, Chinese poet and official (d. 852)
Emma of Altdorf, Frankish queen (or 808)
Ibn 'Abd al-Hakam, Muslim historian (d. 871)
Liu Congjian, Chinese governor (d. 843)
June 24 – Higbald, bishop of Lindisfarne
August 9 – Irene of Athens, Byzantine empress
Ja'far ibn Yahya, Persian vizier (b. 767)
Kardam, ruler (khan) of the Bulgaria (or 802)
Year 803 (DCCCIII) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar.