The Isaurians were a tribe that lived in Anatolia from classical times well into the first millennium AD. They frequently raided surrounding towns in southwestern Anatolia, being known as the scourge of Asia Minor until they were defeated by Justinian.
What if the Huns decided to recruit the Isaurians, or the Isaurians decided to rise up during the Hunnic invasion?
What if the Sassanids decided to recruit them against Constantinople?