 In thanks for the lifting of the siege and the supposed divine protection granted by the Virgin Mary, the celebrated Akathist Hymn was written by an unknown author, possibly Patriarch Sergius or George of Pisidia.After failing to capture Constantinople, the Avars rapidly began to decline before disintegrating entirely, due to both internal power struggles, and conflicts with the Bulgars and Sclaveni.After their hegemony over various tribal peoples collapsed, their land was further reduced by the Bulgars around 680, leaving behind a rump state which remained until their conquest by Charlemagne, starting in 790 and ending in 803.