1. Historical framework

Although it was the Turks who finally toppled the Byzantine Empire, the biggest competitor and enemy of the Empire during its millennium-long existence were in effect the Arabs. It wouldn't be an exaggeration to say that throughout the existence of the Byzantine Empire, no other nation had played such an important role in its history as the population of Arabia. They attacked the foundations of the Byzantine Empire, and shook them hard, and on two occasions at least they threatened the very survival of the great Empire.

Already from its early years, the arabian state's external policy targeted its two great neighbors – Persia and the Byzantine Empire – in its struggle for survival. The first succumbed during the first attack, while the other managed to resist the new assaulters with tremendous efforts. As early as 634, the Arabs succeeded in intruding the region of Transjordan. During the next half century, the Byzantines knew only defeat in their conflicts with the Arabs. One after another, the Empire’s provinces were falling: Syria, Palestine, Mesopotamia, Egypt, the islands of Cyprus, Rhodes, Kos, Chios. Besides, the Byzantine territories in Asia Minor were constantly being ravaged.

Upon review of the geographic location of these regions and especially the islands, it instantly becomes clear that Constantinople was the ultimate goal of the Arabs. The caliph Muawiyah I (661-680) passed on to his son Yazid I his aspirations and plans regarding the Byzantine Empire. In 670, Arabian battalions conquered the Cyzicus peninsula in the Sea of Marmara, Asia Minor. Then the conditions were fully ripe for the Muslim assaulters to move towards the Byzantine capital.

2. First Siege (674-678)

In the spring of 674, an enormous and terrifying Arabian fleet appeared in the shores near Constantinople, under the command of Abd ar-Rahman. The sea was foaming with the numerous ships which gathered in front of the Bosporus straits. When the Byzantine Emperor Constantine IV (668-685) learned of the movement of the Arabs towards Constantinople, he took measures to ensure that the capital would be prepared for the attack. It is worth mentioning that people had been terrified by an event that had taken place in the previous year, 673. As Theophanes has written down, the goddess Iris had appeared in the sky in March, and the whole of humankind was shaking in terror.¹

On the other side, Sufyan ibn Auf, the commander of the Arabian army, had reached Chalcedon. In the meantime, a large battalion came ashore from the Arabian ships to the European land, close to the walls of Constantinople, with the aim of surrounding the city from the land, in the area between the Sea of Marmara and the inlet of the Golden Horn. And precisely the simultaneous encirclement of Constantinople from both the land and the sea, regardless of its fortified walls and good defense system, represented the biggest danger for the megalopolis on Bosporus. At the same time, the inlet of the Golden Horn was the weakest spot in defense and the “soft belly” of the Byzantine capital.

As for the surroundings of Constantinople, bitter battles were fought between the Byzantines and Arabs throughout the summer of 674, until the autumn, when the weather conditions didn't permit sailing and warfare any more, and consequently the Arabian fleet withdrew to their winter harbor in Cyzicus. This withdrawal gave the Byzantines the precious opportunity to replenish their supplies and repair the city walls that had been partly damaged by the enemy. The Arabian siege was reprised for no less than five years: in 674, 675, 676, 677 and 678. Time and again, however, the strongest fortress of the medieval world stood fast and did not fall.

The Byzantines owed their enormous success primarily to the new invention, the so-called “Greek Fire,” a true marvel of the medieval military technology and engineering. It was actually the liquid flame which was being released under pressure from the special tubes, the so-called strepta, and caused fire on the ships.² According to the traditional belief, based on the information from Theophanes's chronicle, which is today mostly disputed, the Greek Fire was an invention of the architect Callinicus from the town of Heliopolis in Syria (or perhaps Egypt). In 673/674, he brought this dangerous weapon to Constantinople, which turned out to be life-saving for the Byzantines, tipping the scale and securing the victory of the Byzantines over the Arabs. The exact chemical composition of this incendiary device, which helped the Romans win a series of military battles, has never been determined, but it was believed that its main component was niter.

Theophanes wrote that the Byzantines had won the victory over the Arabs under the walls of Constantinople with the help of God and Virgin Mary. He added that those believing in Allah had to withdraw in great trouble and with deep and big wounds. However, this was not the end of their misfortunes: a strong tempest caught the Arabian ships near the shores of the region of Pamphylia in Asia Minor, just close to the town of Syllaion, and completely decimated their fleet. And, finally, the Arabian army was also defeated on land by the Byzantine troops led by the commanders Florus, Petronas, and Cyprian. It has been reported that as many as thirty thousand Arab soldiers were killed.

After this twofold disaster, the old caliph Muawiyah had no other choice but to sign a peace treaty with the Byzantine emperor Constantine IV, to last for thirty years. He committed to paying the Emperor three thousand gold coins a year and to sending him fifty slaves and fifty horses each year.

Naturally, this great Byzantine victory made a strong impression to all of the contemporaries and echoed throughout the medieval world. It is known that many contemporary rulers sent their emissaries to Constantinople with rich gifts for Emperor Constantine IV, asking him for peace and friendship. The chronicler Theophanes concluded his account of the first Arabian siege of Constantinople with the following line: “And the great carelessness in both East and the West has begun.”³

The modern researchers insist that the Byzantine victory from 678 was of immeasurable significance. It came in the right moment, and a critical one at that, since, after exactly fifty years of almost incessant wars, during which time the Byzantine Empire had not won any greater victory, the Arabian invasion was finally halted. It was a turning point from the perspective of the world history, and Constantinople, as the last barrier to the Islamic invasion, managed to resist, which spared not only the Byzantine Empire but the totality of the then Christian European civilization.

3. Second siege (717-718)

In spite of the actual disaster that the Arabs faced under the walls of Constantinople in 678, the caliphate did not stop aspiring of conquering the Byzantine capital. Thus, four decades later, with the conditions changed for the Byzantine Empire, the Arabs undertook the second siege of Constantinople. The period that preceded this siege was particularly convoluted and difficult for the Byzantine Empire. These were dark times for them, when the Empire lost its balance and had been sinking in a series of devastating civil wars. In the period between 695 and 717, in only twenty two years, there were as many as seven changes at the throne in Constantinople. It was only in the beginning of spring of 717 that the mighty military commander Leo, strategos of theme of Anatolikon, put a stop to the dangerous disintegration of the Byzantine Empire and started his own Isaurian dynasty. However, only a few months later the new emperor was faced with a very difficult task. An enormous Arabian fleet arrived at Constantinople, which, according to Theophanes, consisted of as many as one thousand eight hundred vessels. One of the most terrible years in the history of the Byzantine capital began.

In order to fully understand the events that followed, it is important to insist upon the fact that, at that time, the Arabian Caliphate was surpassing the Byzantine Empire in strength and military means. The Muslim world was spreading from the Indus to the Atlantic Ocean and, particularly after their successful invasion on European soil, the Iberian Peninsula, they felt immensely confident and convinced that there was no enemy left capable of resisting them. The Caliph Suleiman (715-717) sent his brother Maslama, placing under his command the best army that the Arabs had ever put together.

Simultaneously with the arrival of the enormous Arabian fleet, Maslama transferred the army over the Helespont to the European provinces of the Byzantine Empire, in the region of Thrace. This army was marching along the shores of the Sea of Marmara and, having easily conquered some of the cities along their way, they came under the walls of the “Empress of the Cities” on August 15, 717. Thus the Arabian forces laid their siege of Constantinople both by land and sea.

The commander of the Arabian forces, Maslama, ordered a moat to be made around the city lland walls and a tall wall to be built, above which he erected a stone barrier. On the eve of September 1, 717, large Arabian ships arrived, with the task to cut the capital off from its connection with the European regions, but also with Asia Minor and the Black Sea. In essence, Maslama carried out a complete blockade of the Byzantine capital because he believed that by exhaustion and hunger he would manage to yield the morale of the defenders and thus he would conquer Constantinople.

The siege of Constantinople lasted one full year, since, unlike the 674-678 siege, it was not interrupted during the winter. In an attempt to explain the Arabian failure and the unbreakable will of the defenders, the chronicler Theophanes reports that the recently-coronated emperor Leo III (717-741) had previously won a tremendous diplomatic victory over the Arabian leader. A few months before the siege, the new emperor, who spoke excellent Arabic and participated in the negotiations with the Caliph Suleiman and his brother Maslama, had been stalling the negotiations in Asia Minor. So it happened that, since his coronation in March until the beginning of the siege in August 717, there had passed five months which Leo III had used in the best possible way to prepare the defense of Constantinople. The fact that the Islamic warriors commenced the siege only in mid August, which was considered rather late in terms of the medieval warfare, speaks for itself.

Besides, the land- and sea walls of the city were in very good condition, while the Byzantine navy held the protected harbor at the Golden Horn. And the famous chain should definitely not be omitted: this chain, a weighting a few tons, prevented any enemy ships from entering the Golden Horn, the most sensitive defense point of Constantinople. The necessary provisions were collected and stored in time, and the constantinopolitan authorities had also had a deal with the Bulgarians, who had promised to harass the Arabian troops with sporadic attacks. The Byzantine forces were significantly less than those of the Arabs, but they had precious advantages in skills and techniques.

It was turning out that the clash of the two fleets would be decisive for the fate of Constantinople. Leo III first patiently waited for the favorable winds and sea streams in the Bosporus strait, and only then did he send his large war ships, stored with large supplies of the Greek fire, towards the enemy ships. The Arabs simply had no response to the mercilessly efficient and terrifying weapon of the Byzantines. A part of their fleet sunk at the bottom of the sea, the other part, caught by fire, was pushed towards the city walls, while the third part was pushed towards Oxeia and Plateia, the islands some thirty kilometers away from Constantinople. However, not even that affected the perseverance of the Arabian leaders and their soldiers. They responded by sending their elite squadrons, fully equipped, aboard the ships to assault the sea walls of Constantinople. The garrison of Constantinople prevented this heroic attempt of the Muslim warriors by using the Greek fire, which they were throwing from the city walls on the attackers. Moreover, Leo III ordered that the chain closing the entrance to the Golden Horn be released at the critical moment, but the Arabs, fearing that it was a trap, did not even dare to sail into the bay. Instead, they withdrew their ships and thus acknowledged the defeat at this stage of the conflict.

The Arabian troops were also rather disturbed by the news that on October 8, 717, their caliph Suleiman passed away. He had been very eager and confident about this invasion, and his loss was a blow to the morale of the Arabs. Nonetheless, not even winter stopped the siege, though the attackers, after the defeat of their fleet, could only rely on their army troops. The sources report no major battle until the very end of the autumn. It should be added that the Byzantines had surpassed for centuries all other medieval nations in military architecture and the engineering, which gave them considerable advantage at this point.

However, the biggest problem for the Arabs was actually the climate, which they had simply not been used to. The winter of 717/718 was reportedly one of the coldest ones in the Byzantine history. Constantinople was covered in snow and ice for more than a hundred days in a row, and consequently, a large number of camels and horses died of hunger in the attackers’ camp. The Muslim soldiers, used to the warm and dry climate of their homeland, could hardly bear the famously icy winters in Thrace. And this was one of the most important reasons for their failure at Constantinople. Already by the end of 717 it was becoming clear that the seizing of the “Empress of the Cities” would remain an unattainable dream for the Arabs. The spring of 718, instead of providing some relief, only brought with it new troubles and the endeavor which started with such high hopes turned into a complete disaster.

In the first months of 718, the attackers received great reinforcements: one fleet, consisting of four hundred ships, sailed from Alexandria and reached Bosporus; the other, consisting of three hundred sixty vessels, carrying military equipment and food supplies, came from Africa. However, both fleets stopped short before reaching Constantinople because they feared the Greek fire, which resulted in their diminished efficiency in aiding the exhausted and above all discouraged compatriots.

It also happened that the Arabian sailors, recruited mostly among the Egyptian Christians, having realized that the success is difficult to attain, defecteded to the Byzantine side, and not only that, but they also provided Emperor Leo III with detailed information on the location of the enemy ships. Without any hesitation, the emperor ordered that Byzantine ships equipped with the Greek fire immediately sail out of the constantinopolitan harbor and attack the enemy. This was a completely successful endeavor: part of the Arabian ships was destroyed by fire, another part was sunk, and a number of ships were captured. The Byzantines took the loot and food supplies and joyfully returned to Constantinople, according to the chronicler Theophanes's conclusion in the description of this event.

The Arabian army was trying their best to keep hold of Thrace, but they were suffering from provision shortages, both for the army and for the animals. Their attempts to send individual squads in search for basic supplies were cut short upon their return. Precisely in this aspect, a key role was played by the battalions of the Bulgarian ruler Tervel (701-718), who systematically assaulted the Arabs, putting them under constant threat. Their efforts took from the Arabs a toll of as many as twenty two thousand dead soldiers.

In the camp of the Muslim warriors there was hunger, followed by various diseases, which caused the death of thousands of Arabs. As the chronicler Theophanes reported, they ate all their dead animals – horses, asses and camels – and some said that they even took the deceased people and their excrements and first they would put them in the dishes, then grind them, and finally they would eat that mixture. Such exaggerated descriptions clearly depict the desperate condition that the Arabian troops were in. Theophanes’s Chronicle also reports the attackers' convinction that God and the Virgin Mary were protecting Constantinople and the Christian Empire.

As these troubles decimated the Arabs and clearly affected their morale, on the other side, they encouraged the defenders of the capital on Bosporus and made them braver and more aggressive, to the extend that they started attacking the confused enemy. At the same time, in order to make the defeat of the Caliph’s troops complete, Byzantine troops ambushed and managed to defeat the new-coming troops arriving to aid the attackers. Having realized that the endeavor had infamously failed, the commander of the Arabian army lifted the siege and began to withdraw his troops. On the other side, inside Constantinople, on August 15, 718, there was enormous joy because the deadly danger which had lingered above Bosporus for exactly one year was finally removed.

As with the return from the siege of 678, this time as well the great number of the Arabian ships was not destined to reach the safe harbors on the shores of Eastern Mediterranean. After a series of troubles and losses, only five out of one thousand eight hundred ships that were participating in the siege, reached the shores of Syria. A similar fate met the army troops which, after disembarking on the Asia Minor shores of the Sea of Marmara, returned to their homeland by land. If the preserved sources are to be trusted, although they carry only brief and fragmentary information, the Arabs lost over one hundred thousand soldiers at the siege of Constantinople. The provided information, as well as the consequences of this famous event, put the siege of the Byzantine capital among the most important events of medieval history.

One of the pioneers of the modern Greek Byzantine studies, Spyridon Lambros (1851-1919), compared the siege of Constantinople from 717/718 with the Greek-Persian war and he named Emperor Leo III "Miltiades of medieval Hellenism".

4. Assessment