|Covid-19|Byzantine–Bulgarian Treaty: Emperor Leo V the Armenian signs a 30-year peace agreement in Constantinople with Omurtag, ruler (khan) of the Bulgarian Empire. The Rhodope Mountains become the Byzantine border again, and Leo regains its lost Black Sea cities, after the Bulgars have them demolished.
Hrafna-Flóki Vilgerðarson sets out from the Faroe Islands and discovers Iceland (documented later in the Landnámabók) (approximate date).
King Egbert of Wessex ravages the territories of the remaining British kingdom Dumnonia, known as the West Welsh (Cornwall).
Emperor Saga of Japan is the first sovereign to drink tea (according to legend), imported from China by monks. The upper classes adopt this beverage for medicinal use.
July 13 – Wu Yuanheng, Chinese chancellor of the Tang Dynasty, is murdered by assassins of warlord Wu Yuanji, in Chang'an.
Synod of Constantinople: A council led by patriarch Theodotus I, in the Hagia Sophia, reinstitutes iconoclasm.
Abu Hanifa Dinawari, Muslim botanist and geographer (d. 896)
Boniface VI, pope of the Catholic Church (d. 896)
Dawud al-Zahiri, Muslim scholar (approximate date)
Eberhard, duke of Friuli (approximate date)
Johannes Scotus Eriugena, Irish theologian (approximate date)
Leoluca, Sicilian abbot (approximate date)
Methodius, Byzantine missionary and bishop (d. 885)
Theodora, Byzantine empress (approximate date)
July 13 – Wu Yuanheng, chancellor of the Tang Dynasty (b. 758)
Jābir ibn Hayyān (Geber), Muslim alchemist (approximate date)
Mashallah ibn Athari, Jewish-Arab astrologer
Muirgius mac Tommaltaig, king of Connacht (Ireland)
Omar Tiberiades, Persian astrologer (approximate date)
Sadnalegs, emperor of Tibet (approximate date)
Year 815 (DCCCXV) was a common year starting on Monday (link will display the full calendar) of the Julian calendar.