Today in European history: the Siege of Constantinople begins (maybe, 717) and ends (718)

The Byzantine Empire survives an Umayyad siege thanks to Greek Fire, a rough winter, and the Bulgars.

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Before it fell for good to the Ottomans in 1453, the city of Constantinople successfully withstood something multiple sieges over its long history. Even the one successful siege, by the soldiers of the Fourth Crusade in 1204, wound up being rolled back when a restored Byzantine Empire supplanted the short-lived Latin Empire in 1261. At least one, and possibly two, of the more famous failed attempts to take the city were made by Arab armies under the Umayyad Caliphate. The first attempt may have been made in 674-678, when the Byzantines may have been saved by the advent of Greek Fire (a highly effective incendiary weapon, whose formula is still unknown, that was particularly destructive at sea because it continued to burn even in water) which enabled them to destroy an Arab naval blockade of the city sometime in 677-678.

The 674-678 affair is considered the Arabs’ “first siege” of Constantinople, though it wasn’t really as cohesive as that description implies. I italicized “may” twice above because there are good reasons to believe that whatever happened in the 670s was not a siege of Constantinople per se and that, whatever it was, it was not ended with the first use of Greek Fire. No record of a siege appears in any eastern sources from the period, and historians only have the writings of imperial chronicler Theophanes the Confessor as evidence that it took place. Many scholars nowadays think that the “siege” was actually a series of unconnected Arab expeditions that Theophanes later misinterpreted as a single campaign.

Anyway, after whatever happened in the 670s the Arabs were soon drawn into their second empire-wide civil war, so for some time the Byzantines found themselves uncharacteristically as the more powerful party in this relationship and were even able to extract tribute payments from the Arabs. But then everybody’s fortunes shifted, and from the 690s through the 710s its was the Byzantines who were dealing with internal strife while Arab armies kept pushing deeper and deeper into Anatolia.

The problem the Arabs had in defeating the Byzantines once and for all was that supply routes over the Taurus Mountains were too difficult to sustain for any length of time, and the Anatolian populace was certainly not about to support an Arab occupation. So for most of the history of Arab-Byzantine conflict the two sides didn’t invade each other’s territory so much as they launched raids. The goal was to hurt the other side and bring back some nice booty, not to take and hold territory, and when the campaign season started to wind down the raiders usually had no choice but to retreat back across the mountains into their own territory. This would be the state of affairs between the Caliphate (and its successor states) and the Byzantines until the late 10th century, when the resurgent Byzantines briefly won back control of northern Syria and Armenia, but then the Battle of Manzikert in 1071 finally opened Anatolia up to Muslim (though now it was Turks rather than Arabs) settlement.

The Umayyad siege of Constantinople 717-718 stands out, then, because it was very much a serious attempt to conquer the Byzantine Empire, not a mere raid. This was, of course, much easier said then done. There’s a reason why Constantinople survived as many sieges as it did and why it took the Ottomans, armed with massive siege cannons, to finally capture the city.

The Theodosian Walls, built in the 5th century, were so massive that it took 15th century guns to finally breach them. The Arabs of the eighth century, who were still new to siege warfare in general, didn’t have a chance of breaching them and they knew it, so their plan instead was to blockade the city by land and sea simultaneously and simply wait the Byzantines out. This was not, as we will see, a recipe for success.

It was during the reign of the Umayyad Caliph Sulayman (d. 717) that plans for a new siege of Constantinople really took shape, under the direct command of the caliph’s brother, Maslama b. Abd al-Malik (d. 738). But the plan required a naval blockade, and a naval blockade required a navy, and the Arabs didn’t have much of a navy at this point. So they were forced to build some, and all that ship-building was hard to keep under wraps. Byzantine agents picked up on the activity starting in about 715, and consequently the empire had lots of time to strengthen Constantinople’s fortifications and stock the city with plenty of supplies. Their preparations were hampered, however, by the fact that the Byzantine Empire was still in that period of instability that had begun in the 690s that I mentioned earlier. Between 715 and 717, shortly before the siege began, the empire changed hands twice, from Anastasius II to Theodosius III and finally to Leo III (d. 741), who took power in March 717 and ruled for almost a quarter of a century after that. People who know something about Church history will recognize Leo as the emperor who ushered in Iconoclasm, but we’re not going down that road here. Leo is a key player in our story, though.

The Umayyads were aware of this internal strife and were hoping to exploit it, if not to conquer the empire in full then at least by putting a friendly puppet on the throne. Leo, who at this point was a general in the imperial army, apparently sent word to Maslama that he would be willing to subjugate the empire to the caliphate if the Umayyads could put him on the throne. Theodosius III was not a terribly popular emperor—he’d really been forced by the army to take the job, and he governed like a guy who had never wanted it. Maslama agreed, though it’s likely he planned to double-cross Leo after using him to sew chaos in the empire. Of course, with the benefit of hindsight we know Leo definitely intended to double-cross Maslama. In 716, Maslama and Leo led their combined armies in capturing a fortress in central Anatolia. Once it was secured, Leo promptly garrisoned it with his men and shut the gates to the Arabs. Double-cross achieved. With campaign season almost over, Maslama had to retreat to Cilicia, the coastal pass through the mountains, and Leo was then able to make his way to Constantinople and convince the (probably thankful) Theodosius to abdicate.

The following year, Maslama, with his army and navy in synch, made the final push to Constantinople, besieging the city from land on either July or August 15, 717, while his navy sailed into the harbor. Unlike that alleged siege in the 670s, we know in 717 that the Byzantines made great use of Greek Fire to destroy Arab ships, forcing their navy back out of the harbor and away to a safer distance. At this point, and again with the benefit of hindsight, we can say that with the failure of their attempted blockade the Umayyad siege was effectively over. With the Byzantines free to continue bringing in supplies by sea, a “starve them out” type of siege was doomed to fail. Then Mother Nature decided to compound the Arabs’ problems by making the winter of 718 particularly harsh, which meant that the besiegers ran out of food—even though they had reportedly brought plenty with them and even brought seeds and implements to farm more—and disease ran rampant through their camp.

Arab sources relate that the army ran out of supplies not so much because of the harsh winter as because of a somewhat inexplicable con job by Leo. Leo supposedly sent word to Maslama that he wanted to uphold his end of their original deal and hand the city over to the caliphate, but he needed the Arabs to prove to the people inside the city that their army meant business. Somehow, according to these sources, Leo convinced Maslama to send part of his army’s food supply into the city, to show his great generosity, and to burn the rest, to show Constantinople’s denizens that his army wasn’t going to settle for a siege but was ready to launch an all-out attack. Maslama supposedly did as Leo suggested and, well, we know how that worked out.

Now, it is almost impossible to believe that any human being could this credulous. But as I say, this is a story that’s related in Arab sources—sources that, although they were written much later and under the Umayyads’ successors, the Abbasids, don’t otherwise seem to have been that critical of Maslama. Byzantine sources don’t mention this event at all, and it’s quite possible—even likely—that it didn’t happen, but in that case the question is why the Arab sources felt it necessary to include the story. Possibly they intended to portray Leo as a conniving backstabber taking advantage of the scrupulously honest Arabs, and to explain an otherwise difficult-to-explain Arab defeat, and it only reads to us cynical moderns like a story meant to portray Maslama as an inept rube.

When the weather improved, an Arab supply convoy arrived from Egypt, but because almost every experienced Muslim sailor was involved in the initial expedition, this relief fleet was crewed by Christians with less experience in lengthy, trans-Mediterranean voyages. Those ships in this fleet, the ones that survived the trip and whose Christian crews didn’t defect to the Byzantines, were attacked by the Byzantine navy, again using Greek Fire, and most were destroyed. Likewise, a relief army sent by the new caliph, Umar II (d. 720), was met and wiped out by a Byzantine army.

The Arab position outside the walls of Constantinople became untenable. At some point they fought a major battle against an erstwhile Byzantine enemy, the Bulgars, either because Leo had cut a deal with the Bulgars or because Arab foragers had made the mistake of crossing into Bulgar land during their foraging, and the Bulgars soundly defeated them at the cost of thousands of dead Arab soldiers. That may have been the final straw. On August 15, 718, either one year or 13 months to the day from when the siege began, the Arabs packed up and made for home.

Notice that I haven’t said anything about troop numbers here, and that’s because there’s really no reliable count. The Arabs certainly began the siege outnumbering the Byzantine defenders, but there are Byzantine accounts that have the Arab army numbering in the hundreds of thousands, which is pretty outrageous for an eighth century siege army. Even the casualty counts offered by European sources are in the hundreds of thousands, which is again fairly ridiculous. The Arab army may have numbered in the six digits, but if so it wouldn’t have been much more than 100,000. Between the Bulgars, the hunger, and the disease it’s likely that very few of them made it back home alive.

The successful defense of Constantinople is, for better or worse, important in terms of how European and world history subsequently developed. If we can say that the Battle of Tours (732) was crucial in stopping the Muslim advance into western Europe, then surely the fact that the Byzantine Empire survived the eighth century was equally important in stopping a Muslim advance into eastern Europe—more important, really, because there’s no historical consensus on whether the Muslim army defeated at Tours was really an army of conquest and not just a raiding party. This 717 siege in particular was important in that it was the last time a caliphal army would seriously entertain the idea of capturing the Byzantine capital. It also had repercussions in the caliphate. The failure of the 717 siege and its cost in blood and treasure was one of the causes of the steep decline of the Umayyads and their eventual ouster in 750.