"...We crushed the two horns of Qarin at Thaniyy, with violence unleashed."
[ Al-Qa'qa' bin Amr, commander in Khalid's army]1
When the Persian Emperor received the message of Hormuz regarding the Muslim advance from Yamamah, he organised a fresh army at Ctesiphon and placed it under the command of a top-ranking general by the name of Qarin bin Qaryana. Qarin too was a 100,000 dirham-man. The Emperor ordered him to proceed to Uballa with the new army to reinforce Hormuz, and with this mission Qarin set off from Ctesiphon.
Marching along the left bank of the Tigris, Qarin reached Mazar, crossed the Tigris and moved south along the right bank until he reached the Maqil River. He crossed this river and then another largish river a little south of the Maqil. He had hardly done so when he received reports of the disaster of Kazima. These reports were followed by the remnants of the Persian army which had survived the Battle of Kazima and now came streaming into Qarin's camp under the two generals, Qubaz and Anushjan. The survivors included thousands of Arab auxiliaries; and as is usual in such cases, the two partners-Persian and Arab-began to blame each other for the defeat. Their spirits were not as high as at Kazima; but they were brave, men and reacted more with anger than fear at the reverse they had suffered.
Qubaz and Anushjan were eager for battle again. They and Qarin found it difficult to believe that a regular imperial army could be defeated in battle by a force of uncultured and unsophisticated Arabs from the desert. They did not realise that the Battle of Kazima had been fought with not an uncivilised Arab force but a fine Muslim army, purified and strengthened by the new faith. However, Qarin was prudent enough not to advance beyond the south bank. Here he could fight with his back to the river and thus ensure the safety of his rear. By limiting the possibilities of manoeuvre, he would fight the frontal set-piece battle which the Persians loved and for which their training and discipline were ideally suited.
The remnants of the Persian army of Uballa were followed by the light cavalry detachments of Muthanna; and once contact was established with the Persians, the Muslim horsemen scoured the countryside for supplies while Muthanna kept the Persians occupied and carried out reconnaissances. The Persians made no attempt to sally out of their camp. Muthanna sent a messenger to Khalid to inform him that he had made contact with a powerful enemy force at Sinyy.2
The word sinyy was used by the Arabs to denote a river. Muthanna had contacted the Persians on the south bank of a river, and for this reason the battle which will now be described is called the Battle of the River.
On leaving Kazima, Khalid marched north until he reached some ruins in the vicinity of the present Zubair, about 10 miles south-west of Uballa. He had already decided not to turn towards Uballa, where there was no enemy left to fight, when Muthanna's messenger brought the news about the concentration of Qarin's army and the survivors of Kazima. Khalid was anxious to contact and destroy the new Persian army while the impact of Kazima was still fresh in the Persian mind. Consequently, while he sent Maqal bin Muqarrin with a detachment to enter Uballa and gather spoils (which Maqal did), Khalid marched towards the River with the main body of the army. He caught up with Muthanna in the third week of April 633 (beginning of Safar, 12 Hijri).
Khalid then carried out a personal reconnaissance of the Persian position. Since the Persians had their backs to the river there was no possibility of outflanking them; and Khalid could think of no way of manoeuvring the Persians away from their position as he had done with Hormuz. Khalid accordingly decided to fight a general set-piece battle, in the imperial Persian style. This was unavoidable, because with Qarin poised for action as he was, Khalid could neither cross the river to enter deep into Iraq nor proceed west-wards towards Hira.
1. Ibn Kathir, Al-Bidayah wan-Nihayah, Dar Abi Hayyan, Cairo, 1st ed. 1416/1996, Vol. 6 P. 425.
2. It is difficult to express this word in English. In Arabic it is written as (Yaqut: Vol. 1, p. 937) or as Tabari puts it (Vol. 2, p. 557 )