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The Avar Siege of Constantinople, 626

In 626 Avars, Slavs and Persians besieged Constantinople while the emperor was campaigning a thousand miles away. How the city held, and how the victory was credited to the Virgin.

In the summer of 626 the Avar khagan brought an army of Avars, Slavs, Bulgars and Gepids to the land walls of Constantinople, while a Persian army under Shahrbaraz occupied the Asian shore opposite. It was the first time the city had been attacked by two coordinated enemies from both sides at once, and the emperor Heraclius was not there — he was campaigning in the Caucasus, more than a thousand miles away, and had decided not to come back.

The city held for ten days and the coalition broke apart. The victory was attributed to the Virgin Mary, and the way it was commemorated shaped Byzantine religious identity for the next eight hundred years.

The Situation

By 626 the Roman East had been losing to Persia for twenty years: Syria, Palestine and Egypt were under Persian administration, and Jerusalem had been sacked in 614. Heraclius’s response, described in Heraclius and the last Roman–Persian war, was to ignore the occupied provinces and strike at the Persian heartland from the north.

That left the capital exposed, and the Persians opened negotiations with the Avar khagan, whose confederation dominated the Balkans and whose subject Slavs could supply the one thing the Avars lacked: boats.

The Defence

Command in the city rested with the patrician Bonus, as magister, and the patriarch Sergius, who was both regent for the emperor’s young son and the organiser of the spiritual side of the defence. The garrison was about twelve thousand men — small for the length of wall, but the Theodosian walls were designed to be held by few.

The strategic key was the water. The Persians had no fleet; the Avars’ Slavic auxiliaries had dugout canoes. If the two armies could not communicate or combine across the Bosphorus, they were two separate sieges, neither of which could succeed. Byzantine ships patrolled the strait throughout and prevented any crossing — the single most important fact of the campaign.

The Siege

The Avar vanguard appeared in June; the khagan arrived with the main force and siege engines on 29 July. The bombardment concentrated, as always, on the central sector where the Lycus valley crosses the wall line.

Avar siege towers and rams made no impression. On 7 August the khagan attempted a combined assault: an attack on the land walls simultaneous with a crossing of the Golden Horn by the Slav canoe flotilla, intended to land troops behind the defences at the Blachernae. Byzantine warships intercepted the flotilla in the Horn, in shallow water near the shrine of the Virgin at Blachernae, and destroyed it. Contemporary accounts describe the water full of wreckage and bodies.

With his fleet gone, his assaults failing, his supplies exhausted and his Slavic contingents deserting, the khagan burned his engines and withdrew on 8 August.

The Virgin’s Victory

The interpretation was immediate and unanimous. The patriarch Sergius had carried an icon of the Virgin along the walls during the siege and had paintings of the Virgin and Child set up on the gates. The decisive engagement had taken place in front of her shrine at Blachernae, where her robe was kept as the city’s chief relic.

The Chronicon Paschale, written within a few years, and the poet George of Pisidia, who wrote a verse account called the Bellum Avaricum, both present the outcome as a direct intervention. A story circulated afterwards that Avar soldiers had reported seeing a woman in fine dress walking the walls alone.

From 626 the Theotokos was the city’s protector in a formal, civic sense, not merely a devotional one. The consequences for art are large, and are traced in the Theotokos in Byzantine art: the image of the Virgin as defender of the walls, the Blachernitissa type with hands raised in prayer, and the use of her icons in military processions all follow from this period.

The Akathist

The most durable commemoration is liturgical. The kontakion beginning “To you, invincible champion, I your city ascribe the victory” became the prologue to the Akathist Hymn, and Byzantine tradition connects it to the deliverance of 626. The hymn itself is probably older — sixth century, possibly by Romanos the Melodist — but the prologue is the siege’s, and the all-night standing vigil of the Akathist, still sung on the fifth Saturday of Lent in every Orthodox church, descends from the thanksgiving services held in the city that August.

There is a neat irony in this. A hymn attached to a seventh-century military emergency is now the most widely used Marian devotion in the Orthodox world, sung by people with no idea that “invincible champion” was originally a claim about a specific week in August 626.

Consequences

For the Avars, the failure was terminal as a great power. Their subject peoples began to break away almost immediately; the Serbs and Croats were settled in the Balkans in this period, according to Constantine VII, precisely as a Byzantine counterweight; and the khaganate was destroyed by Charlemagne in the 790s.

For the Persians, 626 was the last chance to win the war by a decisive blow. Heraclius destroyed their field army at Nineveh sixteen months later.

For Byzantium, the siege confirmed a strategic truth that would hold for eight hundred years: as long as the city held the sea and the walls were manned, no besieger without a fleet could take it. The Arab sieges of the following century tested the proposition again and reached the same result.

The Sources

The siege is unusually well documented for the seventh century. The Chronicon Paschale was compiled in Constantinople within a decade and appears to use official records; George of Pisidia was a deacon of Hagia Sophia and a court poet writing for an audience that had lived through the events; and a sermon by Theodore Synkellos, delivered on the anniversary, survives. All three are triumphal and theological in register, and all three agree on the sequence of events and the decisive role of the naval action in the Golden Horn — which is about as much corroboration as a seventh-century event can offer.

The Coalition’s Problem

The alliance between the Avars and the Persians looked formidable on a map and was structurally unworkable, and the reason is worth setting out.

The Persians under Shahrbaraz held Chalcedon on the Asian shore. The Avars and their Slavic and Bulgar auxiliaries held Thrace on the European side. Between them lay the Bosphorus, perhaps seven hundred metres wide at the narrowest point and patrolled by the Byzantine fleet.

Neither force could reinforce the other. Neither could combine for a single assault. The Persians had no ships at all; the Slavs had dugout canoes suited to rivers, not to a strait with a four-knot current and warships on it.

The khagan understood this and tried to solve it on 7 August by using the canoe flotilla to ferry Persian troops across at a narrow point while assaulting the land walls simultaneously. The Byzantine navy intercepted the flotilla in the Golden Horn and destroyed it. With that, the coalition became two separate and individually insufficient sieges.

The whole campaign is a demonstration of the principle that governed Constantinople’s survival for eight centuries: a besieger without naval superiority cannot take the city, however large his army.

The Conduct of the Defence

The division of responsibility during the siege is unusually well documented and illustrates how the Byzantine state functioned in an emergency without its ruler.

The patrician Bonus held military command as magistros, organised the manning of the walls, and conducted negotiations with the khagan — a meeting at which the Avar ruler reportedly seated himself on a throne and had Persian envoys attend to impress the Byzantine delegation.

The patriarch Sergius organised the spiritual and civic side: processions of icons along the walls, the display of images of the Virgin and Child on the gates, and the continuous liturgical round. He had also, four years earlier, put the treasure of the churches at Heraclius’s disposal to fund the campaign, and he acted as regent for the emperor’s young son.

The two functions were not separate in Byzantine understanding. A defence conducted with relics and icons was a defence, and the population manning the walls understood the processions as a military measure. The point is central to how Byzantine warfare worked and is discussed in the Byzantine army.

The Numbers and the Rhetoric

The sources give the Avar host as eighty thousand and describe the Slav flotilla as filling the Golden Horn. Both are rhetorical.

What can be said is that the coalition was large enough to invest a wall line of some five and a half kilometres, that it brought siege towers and engines, and that it sustained operations for about ten days before supply failure and desertion forced a withdrawal. The Byzantine garrison is given as around twelve thousand, which is plausible for the Theodosian walls and consistent with the fact that a small force could hold them.

The withdrawal on 8 August was not a rout. The khagan burned his siege engines — a deliberate act, not a panic — and marched away, and the Avar confederation remained a power in the Balkans for another two decades before its subject peoples began breaking away.

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