Siege of Constantinople (626): Avars and Persians at the Walls

The Siege of Constantinople in 626 was a coordinated attempt by the Avar khaganate and Sasanian Persia to capture the Byzantine capital while Emperor Heraclius was campaigning far to the east. From late June to early August, an Avar-led army attacked the land walls while a Persian army waited across the Bosporus. The defence, led by Patriarch Sergius and the official Bonus, held, and the destruction of the attackers’ boats in the Golden Horn ended the siege. Its failure was a turning point in the last great Roman-Persian war.

Background

By 626 the Byzantine Empire had been fighting Persia for more than twenty years (see Byzantine-Sasanian War of 602–628). The Persians had taken Syria, Palestine and Egypt, while Heraclius had taken the war into Persian territory through Armenia and the Caucasus.

To force Heraclius to return, the Persian king Khosrow II planned a strike at Constantinople itself. He sent his general Shahrbaraz with an army to Chalcedon (modern Kadıköy), directly across the Bosporus. The Avars, a powerful nomadic people who dominated the Danube basin and the many Slav communities around it, were to attack the city from the European side. The Persians had no fleet, so the allies hoped that Slav boats could ferry troops across the strait.

The defenders

Heraclius chose not to abandon his campaign. Instead he sent part of his army back to the capital and dispatched his brother Theodore against a second Persian force under Shahin in Anatolia.

The city was governed in the emperor’s name by Patriarch Sergius and the patrikios Bonus, a senior official, acting for Heraclius’s young son Constantine. Constantinople was protected by the massive land walls built in the fifth century (see Theodosian Walls) and by sea walls along the Golden Horn, the Bosporus and the Sea of Marmara. Its fleet controlled the waters around the city.

The siege

Avar advance troops appeared before the walls around 29 June 626. The khagan, whose personal name is not recorded, arrived with the main army on 29 July. His forces included Avars, Slavs, Bulgars and Gepids. A contemporary chronicle, the Chronicon Paschale, gives a detailed day-by-day account.

The attackers deployed siege towers, catapults and protective sheds against the land walls, concentrating near the Gate of Saint Romanus and the Blachernae district. For about a week the defenders repelled repeated assaults. Negotiations were tried; the khagan reportedly demanded that the citizens leave the city with only their clothes, and the envoys refused.

Meanwhile the Slavs launched small dugout boats, known as monoxyla, into the Golden Horn, while others gathered on the Bosporus to carry Persian troops across from Chalcedon. Byzantine warships patrolled to stop the crossing.

The battle in the Golden Horn

Around 7 August the Slavs in the Golden Horn attempted a combined attack, apparently timed to a fire signal near Blachernae. The Byzantine fleet, which had been told of the signal and may have lured the boats into a trap, closed in and destroyed them. Many Slavs drowned or were killed when they reached the shore, and the Chronicon Paschale reports that the khagan killed some of the survivors in anger.

With his naval plan ruined, the khagan burned his siege engines and withdrew on 8 August, claiming that lack of supplies forced him to leave. Shahrbaraz’s army at Chalcedon could do nothing without boats and eventually retired. Around the same time Theodore defeated Shahin’s army in Anatolia.

Key people

Patriarch Sergius I (patriarch 610–638) was the spiritual leader of the defence and one of Heraclius’s closest allies. He organised processions, encouraged the citizens and took part in negotiations with the khagan. He later became known for promoting the theological compromise called Monothelitism.

Bonus, a patrikios and magister, was the senior official left in charge of the city’s administration and military defence. The Chronicon Paschale shows him directing the garrison, handling the envoys and coordinating the naval forces.

The Avar khagan, whose name is not recorded in the sources, ruled a nomadic empire based on the Hungarian plain since the 560s. The Avars had raided the Balkans for decades and in 623 (some historians prefer an earlier date) had nearly captured Heraclius himself during a meeting near Heraclea in Thrace.

Shahrbaraz was Persia’s most successful general, conqueror of Jerusalem in 614 and of Egypt. His failure to cross the Bosporus in 626 ended his role in the war’s most ambitious plan, and his relationship with Khosrow II later broke down.

The forces involved

The size of the armies is uncertain. Byzantine sources describe the Avar host as enormous, and a figure of 80,000 is often repeated in modern books, but such numbers cannot be checked. The garrison was much smaller, although the troops Heraclius sent back strengthened it significantly, and many citizens helped man the walls.

The decisive advantage of the defenders was not numbers but geography and technology. Constantinople could only be fully blockaded if an enemy controlled the sea, and neither the Avars nor the Persians had a real navy. The Slav dugouts were light craft unable to face Byzantine warships in open water.

Faith, memory and legacy

During the siege Patriarch Sergius led processions along the walls carrying icons of the Virgin Mary and Christ. The people of Constantinople attributed the victory to the Virgin’s protection, especially as the decisive fighting took place near her great shrine at Blachernae.

Contemporaries celebrated the deliverance in literature. The court poet George of Pisidia wrote a poem on the Avar war, and a homily attributed to Theodore Synkellos praised the city’s rescue. Later tradition linked the famous Akathist Hymn to the Virgin with this siege, although the hymn itself is probably older.

Consequences

The failure of the siege destroyed Khosrow’s hope of forcing Heraclius to return. In 627 Heraclius advanced into Mesopotamia, defeated the Persians near Nineveh and brought about Khosrow’s fall in 628.

For the Avars the defeat was a severe blow. Their prestige among subject peoples declined, and in the following decades Slavs and Bulgars increasingly escaped Avar control. Constantinople would face further great sieges, notably by the Arabs in 717–718 (see Arab Siege of Constantinople), and again the combination of walls, fleet and faith would prove decisive.

The deliverance of 626 became part of the identity of Constantinople as a city guarded by the Mother of God. Later sieges, by the Arabs and the Rus, were described in similar terms, and the Akathist Hymn is still sung in the Orthodox Church during Lent with a prologue thanking the Virgin as the city’s champion.

The memory travelled far beyond Byzantium. In 1537 painters decorated the outer walls of Moldovița Monastery in what is now Romania with a large fresco of the siege. They showed the attackers in the dress of Ottoman Turks, turning the ancient victory into a prayer for deliverance from the dominant power of their own day.

Timeline

• 626, c. 29 June: Avar vanguard arrives before Constantinople.
• 626, summer: Shahrbaraz’s Persian army camps at Chalcedon.
• 626, 29 July: The khagan arrives with the main army.
• 626, 31 July – 7 August: Assaults on the land walls.
• 626, c. 7 August: The Byzantine fleet destroys the Slav boats in the Golden Horn.
• 626, 8 August: The khagan burns his siege engines and withdraws.
• 627, 12 December: Heraclius defeats the Persians near Nineveh.

Why it matters

The siege of 626 was the closest the Persian-Avar alliance came to ending the Byzantine Empire. Its failure turned the war in Heraclius’s favour, weakened the Avars and reinforced Constantinople’s reputation as a city protected by its walls, its navy and, in the eyes of its people, the Virgin Mary.