In 504 and 515, they held raids around the Caucasus, which was the Sasanian northern frontier during the rule of king Kavadh I, causing problems to the Persians in their war against the Byzantine Empire.[27] It is considered that the 20,000 Huns led by Zilgibis were Sabirs. They made treaties with both Justin I and Kavadh I, but decided for the former, which resulted with mutual agreement between Justin I and Kavadh I, and the former devastating attack on Zilgibis and his army.[28]