In this spirit, they came upon the bend of the river; and lo! the famous Iwân, or palace, with its great hall of white marble, stood close before them on the opposite shore. ‘Good heavens!’ exclaimed Sád, dazzled at the sight; ‘_Allah akbar!_ What is this but the White Palace of Chosroes! Now hath the Lord fulfilled the promise which He made unto His Prophet.’ And each company shouted, _Allah akbar!_ ‘Great is the Lord!’ as it came up and gazed, wondering, at the great white building, almost within their grasp. But the city was too strong to storm, and Sád sat down before it. Catapults and testudos were brought up, but they made no impression on the massive ramparts of sunburnt brick. The besieged issued forth in frequent sallies; and the siege is mentioned as the last occasion on which the warriors of Persia adventured themselves in single combat with the Arabs. The investment was so strict that the inhabitants were reduced to great straits. The army lay for several months before the city.[286] But it was not inactive in other directions; for bands were despatched throughout Lower Mesopotamia, wherever the great landholders failed to tender their submission. These ravaged the country between the two rivers, and brought in multitudes of prisoners; but, by Omar’s command, they were dismissed peaceably to their homes.[287] Thus, all Mesopotamia, from Tekrît downwards, and from the Tigris westward to the Syrian desert, was brought entirely and conclusively under the sway of Islam. [Sidenote: Persians evacuate western suburb. Dzul Hijj A.H. XV. January, A.D. 637.] The siege at last pressed so heavily on the western quarter, that the king sent a messenger, proposing terms. He would give up Mesopotamia and all beyond the Tigris, if they would leave him undisturbed on the eastern side. The offer was met by an indignant refusal.[288] Not long after, observing the walls no longer manned, an advance was ordered. They entered unopposed; the enemy had crossed in boats, and entirely evacuated the western bank. Not a soul was to be seen. Sád, however, was unable to follow up the success by storming the further capital; for the ferry-boats were all withdrawn to a distance beyond his reach. So the army, for some weeks, was forced to rest; and, occupying the deserted mansions of the western suburb, enjoyed a foretaste of Persian luxury. [Sidenote: CAPTURE OF MEDÂIN. Safar, A.H. XVI. March, A.D. 637.]