Battle of Nehavend (Yarmuk)

Prelude
After his crushing victory over Yazdegird and his Persian host at Qadisiya, Khalid ibn al Walid rested in wake of his victory. He was confident of his victory over Persia; it showed that his soldiers were easily capable of getting to grips with the Persians in close quarter combat. However, he was still wary of his other adversaries, the Byzantine Empire - and consequently did not move from his position in the Jezira until peace has been made with Byzantium by the Rashidun Caliph Abu Bakr in 640.

Accordingly, therefore, Khalid mustered his forces and drove them deep into the heart of Mesopotamia arriving at Nineveh late in the year and taking it bloodlessly. The Persian Emperor, meanwhile, had fled from his base in Nineveh to his capital at Ctesiphon, where he watched operations from between the rivers Tigris and Euphrates. Khalid, after his leisurely pillage and conquest of Western Mesopotamia, converged on Ctesiphon, which Yazdegird and his army of levies, now 20,000 strong, departed from promptly. In the midsummer of 641, the wealthiest city in the East, second only to Constantinople in the world, fell to the Arab hordes. It was despoiled and plundered by the the ferocious Khalid, who was swift in his pursuit of the Persians. He caught up with Yazdegird in the early spring of 642, near the town of Nehavend on the Iranian Plateau.

Yazdegird's Battle Deployment
By a rare stroke of fortune, a quarter of Yazdegird's army was made up of the fabled Clibinarii, who - despite their failings on the field at Qadisiya - were still a forced feared even by Byzantium's best generals. Accordingly, Yazdegird deployed these in two divisions of around 2,500 men each, guarding the flanks. His infantry were drawn up in three lines along the battlefield. In the first line were posted local detachments of slingers and archers, long an asset to the Persian military. The other two lines were made of spear levies from the town communities of the Plateau and Eastern Mesopotamia. A few light skirmish troops were posted in the van - but these alone were not enough to make much impact on the battle.

Khalid Acts
In his turn, Khalid deployed his overwhelmingly superior numbers of lightly armed Arab horsemen on the flanks to serve as a decoy for the Sassanid horse. His heavy cavalry were deployed in a glittering line in the van, supported by Bedouin camel archers and behind them, the Arab infantry. His plan was simple; to carry the Persian middle by weight of numbers and then surround the Sassanid Clibinarii. Accordingly, the Arab cavalry began to march out along the line, accelerating slowly to a full gallop. The sheer number of the cavalry in the centre prevented both the light troops in the van and the slingers and archers in the first line from achieving anything at all. Fleeing the field amost immediately, these soldiers got caught up in the first line of levy spearmen - and were annihilated when the Arab heavy cavalry charged them straight on.

The flank battles went better for the Sassanids; the devastating charge of the Clibinarii gave them a clear upper hand against their lighter adversaries. But the Arabs moved quickly and, gradually as the battle progress, the heavily armoured Clibinarii tired. By the time the Arab heavy cavalry had finished carrying their attack to the second wave of Persian spearmen, the heavily armoured Persian horse were all but spent. The remainder were easily surrounded and cut down.

A Heroic End
Yazdegird, though a fool, could see that there was no winning this battle. Silently he said farewell to his family his friends and his country - and then, without further ado - plunged hither into the melee on the left flank of his army, never to be seen again.

Aftermath
Yazdegird and his army may have fallen at Nevahend, but his son escaped with 1,000 men to try and hold what remained of Persia's empire. Fleeing to Persepolis, the traditional capital of the Achaemenid Persian Empire, he held out for two months before the Arabs assaulted the fortress-like palace town and raised it to the ground. By the early months of 643, all that remained of Yazdegird's empire was a tiny state centred around the city of Merv, which ruled by a Persian, though not Sassanid, dynasty. An indefensible state, it proved to be a diplomatic sticking point between Arabs and northerly Khazars until its destruction by the Seljuk Turks in 1054.