On 27 April 630 Shahrbaraz besieged Ctesiphon with a force of 6,000 men. He was, however, unable to capture the city, and then made an alliance with Piruz Khosrow, the leader of the "Parsig" (Persian) faction, and the previous minister of the Empire during the reign of Ardashir's father, Kavad II. He also made an alliance with Namdar Gushnasp, who had succeeded him as the "spahbed" of Nēmrōz in 626. Shahrbaraz, with the aid of these two powerful figures, captured Ctesiphon, and executed Ardashir III along with many Sasanian nobles, including Ardashir's minister Mah-Adhur Gushnasp. Shahrbaraz then became the new "shah" (king) of the Sasanian Empire, and killed Kardarigan, who opposed Shahrbaraz after his usurpation of the Sasanian throne.