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The Arab conquest of Egypt can be considered the third stage of the early caliphate’s expansion, after its early successes against the Byzantines and the Persians. It also presented a different challenge for the caliphate and its armies. While Egypt may be home to more Arabs than any other country in the world today, in the seventh century very few Arabs lived there, and virtually all of them were transient merchants. The Arabs had initially expanded into Syria and Iraq, places that were already home to large numbers of Arabs. They’d rapidly moved east as the Sasanian Empire collapsed, but the Sasanian Empire was, clearly, hanging by a thread politically. Invading Egypt, a place that was neither hanging by a thread politically nor home to large, potentially friendly population of Arabs, showed that those initial conquests were no fluke.
The invasion of Egypt may also have come as a surprise to the Byzantines. After the Arabs took Syria and set the Sasanian court to flight, the Byzantines seem to have felt as though that would be it for a while, that they might get some time to regroup. Surely the Arabs would need to pacify and consolidate their huge initial gains, right? And that’s got to take some time. The Byzantines probably figured they would have a chance to recover a bit from the double whammy of their devastating plague in the 540s (known today as the Plague of Justinian) and the nearly as devastating 602-628 war with the Persians. Once they’d caught their breath and put together a real, properly trained and prepared army, then they’d see how tough these Arabs really were.
Yeah. So…funny story.
We don’t have great sources for the Arab conquest of Egypt. We don’t have great sources for pretty much any early Arab conquest, really, but it’s especially acute in this case. But we do know that the conquest of Egypt happened a lot sooner than the Byzantines thought it would, and that’s in part due to one Arab commander: Amr ibn al-ʿAs (d. ~664). Like another famous early Muslim general, Khalid ibn al-Walid, Amr was a Meccan who initially fought against Muhammad and his followers before joining the cause in 629 (he and Khalid supposedly went to Medina and accepted Muhammad’s message at the same time). He’s said to have been responsible for “converting” (I hesitate to use that word because Islam was still coming together as a distinct religion in this period, but what can you do) Oman and then governed that region for a short time. Eventually, he joined the Arab armies that invaded Syria and Palestine. He was present, for example, at the Battle of Yarmouk in 636.
In 639, as the Arabs were still picking through the remnants of the Persian Empire, we’re told that Amr asked the caliph, Umar (d. 644), for permission to lead a ~4000 man army into Egypt. Egypt, like most of the rest of the Byzantine Empire, had been walloped by the plague and the war with Persia, during which Egypt was briefly conquered by the Persians. The war was devastating for all the reasons wars usually are, but the restoration of Byzantine control also hurt because, for that brief period under the Persians, Egypt’s Coptic Christians had actually experienced more religious freedom than they were permitted under the orthodox authorities from Constantinople. These folks were not exactly thrilled to see the war end with a Byzantine victory. And the Byzantines were not really ready to defend the place against another invasion, busy as they were trying to beat the Copts back into grudging submission.
One thing that seems to come through in the histories of the Egyptian conquest, spotty as they are, is that Amr knew Egypt to some degree. Again, Egypt wasn’t as familiar to most Arabs as was the Levant, but Amr had spent his pre-military career as a prolific trader and apparently visited Egypt for commercial reasons. As a trader, he may also have had imperial contacts feeding him information. It’s possible, then, that Amr knew how unsettled the province was. He certainly knew how rich Egypt was (the Nile Valley was still the breadbasket of the empire at this point). Whether he pitched Umar with talk of riches or of Byzantine weakness it worked, and the caliph authorized an invasion despite some apparent misgivings (see below). The small size of Amr’s army raises questions about whether it was supposed to conquer Egypt or simply raid it and maybe establish a foothold that the Arabs could later exploit, but I suppose those questions are kind of irrelevant at this point.
There’s a story that has Umar changing his mind about the invasion and sending a messenger to Amr carrying a letter ordering him to turn back—unless, that is, he’d already invaded Egypt by the time he read the letter. Amr, in this tale, has not yet invaded, but realizes what’s in the letter and makes the messenger accompany him as he leads his army into Egypt and then reads the letter. This seems like a legend, but since it’s one that doesn’t make Umar look great in hindsight it’s possible that there’s a kernel of truth to it. It’s funny, anyway. The invasion now a fait accompli, Umar sent Amr around 12,000 additional men, which turned his small expeditionary force into an army that could really do some conquering. Amr met the reinforcements outside the city of Heliopolis.
Heliopolis was located roughly where Cairo is today. In fact, that city’s Ayn Shams suburb is built atop its ruins (its name, which means “eye of the sun” in Arabic, reflects the fact that it was built upon the ruins of the “city of the sun”). One of the funny things about Cairo is that while technically founded in 969, its site has been the location of important cities going all the way back to predynastic Egypt—first Heliopolis, later the nearby fortress at Babylon, and then Fustat, the garrison city that (spoiler) will be founded by Amr as his new provincial capital. All of those places are now part of modern Cairo. Heliopolis wasn’t so important by this point (Babylon, however, was, and that was probably the Arabs’ main target), but Amr decided to make it his temporary base because it was a defensible position with good access to water. It’s here that a ~20,000 man Byzantine army under the command of a general named Theodore decided, for reasons that don’t make a whole lot of sense in hindsight, to meet the Arabs in the open field.
Theodore, it seems to me, had no reason to do this. Amr’s army wasn’t well equipped for sieges and it could have been vulnerable to a Fabian strategy: harass the invaders from your well-fortified garrisons, hoard food inside those garrisons to deny it to the enemy army, then eventually make a major attack on a hungry, exhausted opponent. Theodore opted not to go that route. Worse, it seems he missed opportunities to attack Amr’s smaller force before it met up with its reinforcements. Maybe he was relying on the fact that his army still outnumbered the combined Arab forces to carry the day. If that’s the case then he was wrong, in large part because Amr thoroughly outclassed him in generalship.
The key to Amr’s victory was lots of preparation. The night before the battle, Amr sent a small cavalry force to hide in nearby hills, with instructions to attack the Byzantine flank or rear once the battle started. He sent another detachment south to catch the Byzantines in their anticipated retreat. This all worked pretty much to perfection. The first detachment took the Byzantines completely by surprise and forced them to attempt an orderly retreat toward Babylon, while the second detachment ambushed them during the retreat and turned it into a rout. Almost the entire Byzantine army was killed or captured.
Without going too far beyond today’s topic, Egypt’s conquest at this point was probably inevitable. Babylon was able to hold out for a while—Amr’s army wasn’t equipped for a siege, remember—and capturing Alexandria, Egypt’s real crown jewel, took a while longer, but the Byzantines had just lost a 20,000 man army in one shot and were unable to raise another force large enough to either retake what they’d lost or defend what was still theirs. Amr became governor of Egypt, and founded Fustat when Umar ordered him to base himself on the eastern side of the Nile rather than at Alexandria, as Amr preferred. He lost his governorship in 644, when Umar died and the new caliph, Uthman, appointed a close buddy to the job, but he got it back in 658 as a reward for supporting Muʿawiyah during the First Fitna.