The Arab general Khalid had moved quickly up the Euphrates River in 634, but he left his gains there and went to Syria. Now, with Damascus and Jerusalem securely held by Muslims and the remaining armies tackling the tougher port cities, Khalid was free to go back. What had been happening while he was gone?
While Khalid was gone, the tribal chief Muthanna ibn Haritha was left in charge of collecting the promised tribute. But over the course of a year, the newest Emperor in Ctesiphon was able to recruit and train a new army to face the new threat in the south. Ctesiphon was the Persian capital in the west, not their home base, but the city from which they governed Iraq.
Muslim authority in southern Iraq grew weaker with Khalid gone, and Muthanna asked the Caliph to send another army. Caliph Umar, newly in power, did not find it easy to round up more volunteers. With armies in Syria, they were stretched. But Umar dipped into a reserve that Caliph Abu Bakr had refused to tap: apostates who had rebelled after the Prophet’s death. So they weren’t the best Muslims, so they might be faking faith just to fit in, they can still help fight, right? Eventually, a new Arab army set out for Hirah. This was the former Lakhmid capital that the Muthanna’s men had been occupying.
The attacking and defending armies met across the Euphrates River, with one bridge between them, so it was called “The Battle of the Bridge.” Muthanna pushed his men to be the ones to cross over, forgetting that bridges act as funnels. The army crossing over comes dribbling out, while the army already on that bank can take them out one by one. Pro tip: if you can, always make the other side cross the bridge.
Moreover, on the other side they (the half that had completed the crossing) found that Bahman, the Persian general, had a unit of Indian elephants in his forces. The Arab horses had never seen elephants. The smell and sound of them terrified the horses so that their cavalry was ineffective. In the melée, their commander was trampled. The Muslim fighters were recently recruited, inexperienced, and lightly trained in this type of fighting. They turned to run, but those who had crossed over the bridge mostly ended up in the water, drowning. Crafty old Muthanna had stayed at the back, probably not yet over the bridge, so he lived to fight another day.
The old-model raiding Arabs would have had enough; they would have left off attacking Persia for at least a decade. The Persians were surprised to see that as Muslims, the Arabs had a stronger sense of mission. They were more willing to take losses and try again.
By autumn of 636, two even larger armies faced each other again about 30 miles east of Hirah, on the plain of Qadisiyyah. The top Persian general, a prince named Rustam, was in charge this time. Hugh Kennedy says that he brought along the Persian royal flag, which was 40 meters long and either was made of or looked like tiger skin. A low estimate of Rustam’s force would be 30,000 men, with some estimates ranging to 80,000. They were heavily armed, with even horses wearing chain mail.
The Arab general, Sa’d, probably had no more than 12,000 men (Crawford estimates between 6000 and 12,000). Some forces were called back to Iraq from Syria, and more Arabian tribes were asked to send recruits.
The Battle of Qadisiyah proved to be as decisive against the Persians as the Battle of Yarmouk had been against the Romans. There were many similarities. Both empires were fielding the best army they could, out of an exhausted treasury and new recruits. In both battles, the sides fought conventionally with infantry assaults and cavalry charges, and they were fairly well matched. Both battles lasted for several days. At the Battle of Qadisiyah, the decisive action was Sa’d’s when he chose to push his men to attack yet again when they had been fighting literally all night. Rustam assumed that with a battle ending at daybreak, nobody would be fighting for half a day. The Muslims pushed ahead and attacked unprepared, resting Persians, and one unit ran straight into the center and killed Rustam himself. Then the cavalry pursued fleeing Persian soldiers and cut them down. “Much like Vahan’s army, the force that Rustam led out from Ctesiphon ceased to exist.” (Crawford, 144)
Rustam’s death and defeat left the Persian heartland wide open. There might be smaller army units here and there, but the crushing imperial mega-army was gone. Within a month, the Muslims were advancing on the capital, Ctesiphon, which was on the Tigris River a bit north of where Baghdad is now. An advance force swept most resistance out of the way, until 10 miles from Ctesiphon, a pre-battle set of single combat duels killed the Persian general.
Ctesiphon was a cluster of cities around the Tigris River, so it could not be fully surrounded, the way Damascus had been. It was heavily defended from attacks from the north, but the south had always been guarded by the rivers. There was no bridge, and all ferry boats could be collected on the far side. The Muslims were stopped for the moment by the Tigris River, and there was a stand-off. The Persians had dug ditches around the city they were defending, and they had catapults. But some of the Arabs had used siege engines at Khaybar, and now they got Persians to make a set for them, too. The Persians fell back to Ctesiphon itself, but the Muslims found a point where the Tigris could be forded. They began landing men on the north-east side.
Ctesiphon was not defensible from the south. Emperor Yazdgerd and his army chose to take the bulk of the money in the treasury and flee into the Iranian interior. Sa’d occupied the palace and set up a mosque under the great royal arch. Fleeing Persians had left behind houses, flocks, businesses and treasures.
- The War of the Three Gods, by Peter Crawford.
- The Great Arab Conquests, by Hugh Kennedy