Old Great Bulgaria
The Slavs allied with the Avars invaded and destroyed much of Moesia in 583–587 in the Avar–Byzantine wars. Moesia was settled by Slavs during the 7th century. Bulgars, arriving from Old Great Bulgaria, conquered Lower Moesia by the end of the 7th century. During the 8th century the Byzantine Empire lost also Upper Moesian territory to the First Bulgarian Empire.