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  • James Houser

August 20, 636 - The Battle of Yarmouk & the Arab Conquest

Updated: Jun 13, 2021

August 20, 636 AD. You wouldn’t think the armies of the mighty Byzantine Empire, which has just broken the Persians in a decade-long war, would have much trouble with a bunch of desert nomads. The Arabs, though, are now highly motivated by a new religion founded by their recently deceased Prophet Muhammad. The Battle of Yarmouk will begin the process of the Arab conquest that created the modern Middle East.


At some point later this year, I plan to talk more about the enormous Byzantine-Persian War that lasted from 602 to 628 and nearly destroyed both empires. But today I have to give a quick and dirty rundown of the whole series of events that led to the Arab conquest, since almost no one knows much about this period of history. This is the period of “Late Antiquity” in much of Europe, the hinge between the ancient and medieval worlds, and – despite being barely a blip in the consciousness of most people – one of the critical eras of world history.


For historians, Late Antiquity begins when the Roman Empire begins to first show its signs of collapse, and ends when the birth and rise of Islam completely changes the culture and society of the Mediterranean. It’s a fascinating, vibrant period that gets unfairly skipped over in history class. (But then again, I think EVERYTHING gets unfairly skipped over in history class.)


The Western Roman Empire had fallen to Germanic tribes by 476, and this is the event called the “fall of the Roman Empire.” The Eastern Empire, though, remained intact, and still contained the Balkans, Turkey, Greece, Egypt, Syria and Palestine. The Eastern Empire actually had some of its best years in the 500s AD, with the reign of Justinian from his magnificent capital of Constantinople. Unfortunately for them, by 600 AD a series of plagues and wars had drained the strength of the realm, and it was moving increasingly farther from its Roman and Latin roots. Embracing Greek as a court language, assuming the trappings of Orthodox Christianity, and becoming decidedly more eastern in its outlook, the court at Constantinople no longer looked like the court of Augustus Caesar, or even Constantine. It was something completely different now – something we call Byzantine. Hence, the Byzantine Empire.


The Byzantines had a rival. To the east, occupying modern-day Iraq, Iran, Central Asia and the Caucasus was the Persian Empire, led by the Sassanid Dynasty. This was NOT the ancient Persian Empire that had fought the Greeks, but another entity entirely that had risen in the 200s AD to make trouble for the pre-fall Roman Empire and later for the Byzantines. The Sassanid Persians were a powerful and fearsome entity that followed the Zoroastrian faith, which centered on a dualistic relationship between good and evil. Its ideas had a lot in common with very early Christianity and messianic Judaism, with a Persian mythological tint and a few dashes of Buddhism – basically, a fascinating faith that still exists today in small pockets throughout India and Iran.


The religious situation of Late Antiquity was, to be honest, straight up nuts. Christianity was still in the midst of figuring its business out, with multiple church councils and decrees that culminated in widespread turmoil between the various sects and newly born denominations. This is where that old Monophysite-Miaphysite controversy springs up, and lemme tell you, that is like five posts on its own. Zoroastrianism was having its own flux, though, and even Judaism was a place of fierce debate with multiple scholarly factions in sharp disagreement. Then you still have old Greek Pagans running around, and ideas about the nature of the world and of God are just on everyone’s mind. These play some part in what happened in 602.


From 602 to 628 AD, the Byzantines and the Sassanids found themselves in a cataclysmic, life-or-death struggle. The decades-long Byzantine-Sassanid War was horrifically destructive, and at first the Byzantines were losing badly, seeing Egypt, Syria and Turkey overrun and Constantinople itself besieged. Under the leadership of the Emperor Heraclius, though, and rallied by a resurgence in Orthodox faith, the Byzantines staged a comeback and finally crushed the Persians in northern Iraq. The peace treaty restored the status quo, but both empires were utterly exhausted, drained, and demoralized. The ironic thing was that the seemingly apocalyptic war, which seemed like the worst thing ever, wasn’t even the worst thing that would happen to either empire that century. Because something was a-brewin’ down south in the Arabian Peninsula.


If I have not foreshadowed it enough, that cocktail of religious ideas had trickled down to a small city called Mecca, where a merchant named Muhammad had a vision. At the same time as the Byzantines and Persians were beating each other to death across the mountains of Turkey, Muhammad had founded a new faith called Islam. In 630, a couple years after that war ended, he captured Mecca from its pagan rulers, and even before his death in 632 the Muslims had fought their first skirmishes on the border with the Byzantines. And now we are caught up.


Much of the historical information about this period – especially the Arab conquests – come from very sketchy and untrustworthy sources. Many of the Islamic sources were written decades after the event, and due to the holy nature of many texts historical criticism has not been able to penetrate their facts. Similarly, Byzantine and Persian primary documents are almost nonexistent, so the story is mainly told through Arab eyes. Here’s what we have.


It’s still unclear WHY the Arabs set out on their great conquests. Much has been made (especially since 9/11) of “Muslim aggressiveness,” especially by Western conservatives, so much that it has served to obscure the essential fact that early Islam was quite a militaristic religion and expanded at the point of a sword, whatever its later and more peaceful incarnations. The early Muslim leaders certainly believed in the necessity to conquer the world and submit it to Allah. To be fair, this is the Medieval age, and no one really needed a good reason to go attacking someone else; modern scholars just tend to be tense about this interpretation because it implies a religious war. Well…yes. Despite Facebook memes that have told me otherwise, most wars – even “religious” ones – were not really about religion. THIS one was.


Muhammad had been the Prophet, and at his death some might have expected the new community of Islam to fall apart. What is incredible is that it did not, and at Muhammad’s death it began to spread. He was succeeded as its leader by his father-in-law Abu Bakr, who only lived for two years but managed to unite the whole of the Arabian Peninsula. Since there was only one Prophet, Abu Bakr assumed the title of Caliph, meaning something like “steward,” and implying that they were Muhammad’s successor but not his equal. After Abu Bakr’s death in 634, he was succeeded by Umar, who was controversially not a member of Mohammad’s family but instead a major political mover within the Meccan community. It was the Caliph Umar who would oversee the first great wave of Islamic conquests across the Middle East.


Abu Bakr had believed the main fight would be with the Byzantines in Syria and did not want to launch a major invasion of Persia. Indeed, there is a lot of reason to believe that the initial Arab conquests were just attempts to strengthen the borders; once the Arabs realized they were pushing at an open door, it snowballed into a full-blown conquest. The tip of the spear for these conquests would be one of my favorite lesser-known historical figures: Khalid ibn al-Walid.


Khalid ibn al-Walid is a guy I wish I had more time for, because he may have been one of the greatest generals to have ever lived, a true strategic and tactical wunderkind who was literally never defeated in almost 100 battles. He was also controversial, first because he had led the Arab resistance to Muhammad before he converted to Islam, and second because he was unscrupulous and cruel in his personal ambitions. Throughout his life, he would never be entirely trusted – especially not by Umar. Part of the reason for this distrust is that he MAY or may not have invaded Sassanid-ruled Iraq basically because he wanted to: it would enhance his own prestige and fill his pockets. Khalid was the greatest Arab general, the “Sword of Muhammad,” – just don’t turn your back on him, because he will do what he wants.


Nevertheless, in 633 – still during Abu Bakr’s reign - Khalid took his army up from Arabia into Iraq, following the same route that Norman Schwarzkopf would take in Desert Storm 1,357 years later. Once he got there, he basically just started kicking apart every army the Sassanids sent his way. Reinforced by local Arabs that he was (ostensibly) there to “liberate,” he plundered his way up the Euphrates and just obliterated everyone in his path. He also showed un-Muslim cruelty, crucifying captured Christian prisoners and straight up pillaging every town he took. Brilliant, yes; nice guy, no.


Either way, Khalid was still messing around in Iraq when he got word that Abu Bakr needed his help. The main focus for the Caliphs had been Byzantine Syria, and an initial stab at conquest there had run into trouble in a hurry. So while Khalid had some of the best Arab warriors busting up Sassanian armies in Iraq, the Byzantines had responded to the sudden appearance of the Arabs and concentrated a whole bunch of troops in the area. The local Arab commander, Abu Ubaidah, was inexperienced and suffered reverses. Abu Bakr ordered Khalid to come assist Abu Ubaidah in the conquest of Syria. He needed his best commander leading the most difficult campaign; according to the Muslim chronicles, Abu Bakr said "By Allah, I shall destroy the Romans and the friends of Satan with Khalid Ibn Al Walid." (Reminder that everyone in this period still called the Byzantines “Romans,” since “Byzantine” was a later invention by historians.)


Khalid set out from Iraq to reach Syria. There were several routes that would avoid the truly enormous stretch of desert that lay across his direct path, but each of these routes would slow him down by weeks in coming to the aid of his comrades. Instead, Khalid crossed the vast Syrian desert – a feat that can be compared to Hannibal crossing the Alps in terms of complexity and daring. Khalid’s army at one point marched for two days without a single drop of water, and men, horses, and camels all suffered alike. But in June 634, Khalid emerged from the desert like a thunderbolt. His move had not just been quick, but an ingenious strategic maneuver, completely unhinging the Byzantine defensive lines in Syria and coming out well to the rear of the Byzantine armies.


Khalid used this strategic coup to tactical advantage, immediately taking command of all Arab forces in the area and launching a series of sledgehammer battles that captured city after city. The campaigns are too numerous and complicated to recount here; all that needs to be said is that on July 30, 634, the Arabs with about 10,000 won a big victory over the Byzantines with 40,000 at Ajnadayn, leaving Syria wide open for the taking. Within months, they had entered Damascus itself.


At this point, though, Caliph Abu Bakr had died and Umar had taken command. Umar distrusted Khalid immensely, so his first move was to relieve the brilliant general and replace him with Abu Ubaidah. Khalid showed remarkable loyalty in staying on to serve as a subordinate under Abu Ubaidah. In reality, Abu Ubaidah was basically in awe of Khalid and did everything he said, so Khalid was still mostly in charge. Between the two of them, throughout 634 to 636, the Arabs took city after city across Syria and Palestine. Only Jerusalem still held out, but by now the Byzantines were mustering a counterattack.


Heraclius had finally reacted to this totally unforeseen emergence of some crazy bunch of desert nomads from nowhere. He had reorganized his army, and sent an enormous and well-armed force down south to defeat the Arabs once and for all. In 636, this army slowly began pushing south, causing Abu Ubaidah and Khalid to abandon Damascus and draw their troops in for the decisive battle: the one that would decide the fate of the Middle East.


The battle would take place north of the Yarmouk River, near the modern Golan Heights – the fault line between Syria and Israel to this very day. This position placed the Byzantines in a river valley, allowing the Arabs to dominate the high ground and constantly pelt the Roman armies with spears and bows, diminishing their morale and weakening their resolve. This battle went on for a month until August 19, 636, when the Byzantines advanced to force an end to the Arab upstarts once and for all.


Khalid (not in charge, but really in charge) had his infantry up front, with cavalry held in reserve in the rear. As the heavy Byzantine legionaries pushed forward, they crushed into the Arab center until the Muslim forces fell back. The Byzantines surged forward, reasoning that this was the moment of victory, until they came upon the Arab camp. Khalid had circled his wagons and hobbled his camel herds to form a series of defensive perimeters atop the hill. As the Byzantine cavalry foundered on this obstacle, they were slaughtered by Arab archers emerging from hidden trenches.


Even worse for the attackers, Khalid slipped his veteran cavalrymen between the gap formed by the onrushing Byzantine center. This move caused confusion and separated the wings of the Byzantine army, which could easily be dismantled and scattered. Finally, Khalid made his last move; he led a nighttime operation – almost unheard of in the age before electricity – to seize the bridge into the Yarmouk valley that formed the Byzantines’ only route of escape. Finally, the next day – August 20 – the Arabs assaulted the Byzantine camps. Their foes were forced into a panicked retreat, only to be brought up short at the ravines of the Yarmouk. The Byzantine army was completely destroyed, and the Arabs utterly victorious.


The Battle of Yarmouk had shattered the Byzantine hold on Syria and Palestine, and the next several years saw the Arabs sweep the land. Antioch, Aleppo, Jerusalem, and Gaza fell, all at the hands of Khalid ibn al-Walid. Within the same decade, the Sassanids would be overrun by other Arab armies, and by the 640s the Arabs had overrun Egypt. The Byzantines, reeling, barely managed to survive the Muslim onslaught; the Sassanids did not. Within 20 years after Yarmouk, the Sassanid Empire ceased to exist.


Ever since Yarmouk, the lands now known as the Middle East have been ruled not by Westerners, but by Arabs; the people of those territories have largely followed the creeds of Islam, not Christianity or Zoroastrianism. So much of world history hinged on the Arab conquests that it’s an honest surprise how little-known they are today, and how much could have gone differently without a brilliant, ruthless general in charge of the Arab armies.


The Middle East was born in the shadows of history, where textbooks fear to tread. It’s honestly one of my favorite periods, and you can tell I’m just pleased as punch to talk about it.


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