Byzantine emperor Justinian I rebuilt Singidunum in 535, restoring the fortress and city to its former military importance. The city saw a brief peaceful period of about fifty years, but was then sacked with the arrival of the Avars in 584. During Maurice's Balkan campaigns, Singidunum served as a base of operations, but it was lost again in the early half of the 7th century when the Avars sacked and burned Singidunum to the ground. Around 630, the Slavs settled in the area and in Singidunum, coordinated by a Roman fortress commander. By this time, however, the city had lost its importance as a border fortification and was largely ignored by the Slavs, who dominated the area.