Following this Battle, the Arab Muslim armies pushed forward toward the Persian capital of Ctesiphon (also called Madā'in in Arabic), which was quickly evacuated by Yazdgird after a brief siege. After seizing the city, they continued their drive eastwards, following Yazdgird and his remaining troops. Within a short span of time, the Arab armies defeated a major Sasanian counter-attack in the Battle of Jalūlā', as well as other engagements at Qasr-e Shirin, and Masabadhan. By the mid-7th century, the Arabs controlled all of Mesopotamia, including the area that is now the Iranian province of Khuzestan. It is said that Caliph Umar did not wish to send his troops through the Zagros mountains and onto the Iranian plateau. One tradition has it that he wished for a "wall of fire" to keep the Arabs and Persians apart. Later commentators explain this as a common-sense precaution against over-extension of his forces. The Arabs had only recently conquered large territories that still had to be garrisoned and administered. The continued existence of the Persian government was, however, an incitement to revolt in the conquered territories and unlike the Byzantine army, the Sasanian army was continuously striving to regain their lost territories. Finally, Umar pressed forward, which eventually resulted in the wholesale conquest of the Sasanian Empire. Yazdegerd, the Sasanian king, made yet another effort to regroup and defeat the invaders. By 641 he had raised a new force, which made a stand at the Battle of Nihawānd, some forty miles south of Hamadan in modern Iran. The Rashidun army, under the command of Umar's appointed general Nu'man ibn Muqarrin al-Muzani, attacked and again defeated the Persian forces. The Muslims proclaimed it the Victory of Victories (Fath alfotuh), as it marked the End of the Sasanians, shattering the last strongest Sasanian army.