Then the Kurds came under the control of the Rashidun Caliphate and converted to Islam. The Arab Muslim armies came to Kurdistan after they took control of Ctesiphon (the capital of the Sasanian Empire) in 636. This was in the time of Umar, the second caliph of the Rashidun Caliphate. The Muslim armies attacked and overcame the cities Masibezan (near Ilam) and Hulwan (now Sarpol-e Zahab). When the armies of the Sasanian Empire and the Rashidun Caliphate met at Nahavand, they fought the Battle of Nahavand. In the battle, the Rashidun Caliphate's army overcame the army of the Sasanian Empire. The Arab armies also took control of Mosul, Shahrizor, and Urmia by force. Some places surrendered, like Mandali.