August 15, AD 718

Siege of Constantinople (717–718)

Umayyad siege of Constantinople lifted

After thirteen months outside the walls the besiegers left on the same feast day Byzantine tradition kept for the Virgin's Dormition.

15 August 718: the withdrawal

On 15 August 718 the Umayyad besiegers withdrew from Constantinople after roughly thirteen months. Caliph Umar II had ordered the commander Maslama ibn ʿAbd al-Malik to retreat.

The land army began moving back through Anatolia while surviving ships carried other personnel away by sea. Leo III kept the capital.

The date comes from the Byzantine chronicle tradition and coincides with the Dormition feast; Arab narratives give no exact day, though both Theophanes and Nikephoros support the traditional ending.

Why it had become untenable

Famine, disease and a severe winter had worn the besiegers down, alongside Byzantine naval victories, defections from reinforcement fleets and the defeat of an overland relief army.

Bulgar pressure on the besiegers' rear contributed materially, but the sources do not securely date a single Bulgar assault to 15 August. They also disagree on when and why the Bulgars struck — Theophanes and al-Ṭabarī describe attacks on the Arab camp, while a Syriac account has foraging Arabs entering Bulgar territory.

The Bulgar commander is often named as Tervel, though Bulgarian chronological evidence may place his death before the siege.

The numbers, and who supplied them

Theophanes reports 22,000 Arabs killed in the fighting with the Bulgars, crediting people said to be well informed rather than a count he made. The figures of 30,000 and 32,000 come from the much later Western chroniclers Sigebert and Alberic.

During the naval retreat the sources report destructive storms and an extraordinary fiery hail that boiled the sea and sank ships. Reading that as a Thera eruption is an interpretation; the well-attested eruption of Thera came in 726.

Theophanes says five ships reached Syria — a chronicler's dramatic claim, not a verified count of surviving vessels.

Sources

Researched 24 Aug 2026 7 sources not yet audited Traditional date

How this was checked

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Traditional date. This date is the conventional one, not one fixed by a contemporary record.

What the sources leave uncertain

The 15 August date comes from the Byzantine chronicle tradition and coincides with the Dormition feast. Arab narratives supply no exact date, but both Theophanes and Nikephoros support the traditional ending date.
The sources disagree about when and why the Bulgars attacked. Theophanes and al-Ṭabarī describe attacks on the Arab camp, while a Syriac account says foraging Arabs entered Bulgar territory.
Theophanes reports 22,000 Arab dead. The 30,000 and 32,000 figures come from much later Western chroniclers and cannot form a range of contemporary estimates.
The commander of the Bulgar forces is often named as Tervel, but Bulgarian chronological evidence may place Tervel's death before the siege; it could have been a successor.