The Arabs agreed in return for tribute, which Hormuzan accepted.[3] However, he soon stopped paying tribute, and raised an army of Kurds (a term then used to describe Iranian nomads).[3] Umar, who was caliph of the Rashidun Caliphate, responded by sending an army under Hurqus ibn Zuhayr al-Sa'di, who defeated Hormuzan in 638 at Hormizd-Ardashir, and forced the city to pay jizya .[4] Meanwhile, Hormuzan fled to Ram-Hormizd.