 Because of this, the Avars and Slavs were able to raid without resistance, with the Byzantines only being able to harass raiding columns and set small ambushes, rather than forcing a decisive victory or launching a counteroffensive.The Avars took the cities of Augustae, Singidunum, and Viminacium in 583, and a further eight of the nine cities by siege in 586.Many of these sieges relied upon the Avars utilizing both surprise and speed, advantages which they lost after they moved further inland in 587.