Arab Siege of Constantinople (717-718): Leo III Holds the City

The Arab Siege of Constantinople of 717–718 was a combined land and sea assault by the Umayyad caliphate on the Byzantine capital. For about a year a huge Arab army and fleet surrounded the city, but the new emperor Leo III, the city’s walls, Greek fire, a brutal winter and Bulgar intervention defeated them. It was the last and greatest Arab attempt to take Constantinople, and its failure secured the survival of the Byzantine Empire for centuries.

Background and the rise of Leo III

By the early eighth century the Umayyad caliphate, ruled from Damascus, stretched from Spain to Central Asia (see Umayyad Caliphate). Constantinople, the capital of the Christian Roman Empire in the East, was its greatest unconquered prize. Arab forces had already attacked it in the 670s.

Byzantium was in political turmoil. Between 695 and 717 the throne changed hands by force seven times. The caliph Sulayman (reigned 715–717) prepared a massive expedition, entrusting command to his brother Maslama ibn Abd al-Malik, an experienced general.

As the Arab army advanced through Anatolia in 716–717, Leo, the military governor (strategos) of the Anatolikon theme, negotiated with Maslama and played a double game. He then marched on the capital, forced Emperor Theodosius III to abdicate and was crowned on 25 March 717. Leo, a soldier of Syrian origin, had only months to prepare the city.

He stockpiled food, repaired the walls and readied the fleet with siphons of Greek fire (see Greek Fire).

The siege begins

Maslama crossed the Hellespont at Abydos in the summer of 717 and arrived before the land walls of Constantinople in mid-August. His army dug a trench and built a stone wall around their camp, cutting off the city by land. Medieval sources speak of 120,000 soldiers and 1,800 ships; historians regard these figures as exaggerated but agree that the force was enormous.

In early September the Arab fleet arrived and tried to blockade the Bosporus. As heavily laden ships moved up the strait, Leo sent fire ships against them, destroying a number of vessels. Leo had the great chain across the Golden Horn lowered and raised to tempt and trap the enemy, and the fleet never established a tight blockade.

Winter and starvation

In September 717 Caliph Sulayman died and was succeeded by the pious Umar II. The besiegers remained in their camp through the winter of 717–718, which was exceptionally severe. Theophanes records that snow covered the ground for a hundred days.

The Arab army had expected to live off the land and was short of supplies. Horses, camels and other animals died, and the chroniclers describe terrible famine in the camp. Disease followed. Meanwhile the city, supplied by sea, held out.

Reinforcements fail and retreat

In spring 718 two new fleets arrived from Egypt and North Africa, carrying supplies and weapons. Many of their crews were Christian Egyptians, who deserted to the Byzantines and revealed the fleets’ positions. Leo attacked with fire ships and destroyed or captured much of the reinforcement fleet. An Arab relief army marching through Bithynia was ambushed and defeated.

On land, the Bulgars under Khan Tervel, allied with Leo, attacked the Arab forces in Thrace and inflicted heavy losses. Theophanes gives a figure of 22,000 Arab dead, which cannot be verified. Tervel’s state had been founded only a generation earlier (see First Bulgarian Empire).

Caliph Umar II ordered the withdrawal, and the siege was lifted on 15 August 718, the feast of the Dormition of the Virgin, which the Byzantines saw as a sign of divine protection. The retreating fleet was struck by storms in the Sea of Marmara and the Aegean; Byzantine sources claim only a handful of ships reached home, likely an exaggeration, but losses were heavy.

Key people

Leo III (reigned 717–741), born in Germanikeia in northern Syria (modern Kahramanmaraş in Turkey), rose through the army to command the large Anatolikon theme. His defence of the capital made his reputation and allowed him to found a dynasty that ruled until 802. He later issued a revised law code, the Ecloga, usually dated to 726 or 741.

Maslama ibn Abd al-Malik (died 738) was one of the leading Umayyad generals of his time and spent much of his career fighting the Byzantines and the Khazars. Despite the failure at Constantinople, he remained a respected figure and later became a hero of Arabic legend.

Umar II (reigned 717–720) is remembered in Islamic tradition as an unusually pious and just caliph. His decision to recall the army ended a campaign that had become a drain on the caliphate.

Tervel (reigned c. 700–721), ruler of the Bulgars, had already helped Justinian II regain the Byzantine throne in 705. His intervention in 718 showed how the new Bulgarian state had become a significant player in the region.

Why the city held

Historians usually point to several factors working together. The Theodosian land walls were almost impossible to storm without siege artillery far beyond what the Arabs possessed. Byzantine control of the sea, secured by Greek fire, meant the city could be resupplied while the besiegers starved.

Timing and weather also mattered. The harsh winter struck an army living in tents far from home, while the death of Caliph Sulayman removed the expedition’s main sponsor. Finally, Leo’s diplomacy with the Bulgars opened a second front in Thrace that the Arabs could not afford.

The sources

Our knowledge of the siege comes mainly from the Chronographia of Theophanes the Confessor and the Short History of Patriarch Nikephoros, both written about a century later, and from Arabic historians such as al-Tabari. The Greek and Arabic accounts agree on the main outline but differ on details, numbers and the reasons for the defeat. Arabic sources tend to stress the cold, the hunger and Leo’s deception of Maslama, while Byzantine writers emphasise divine protection and the power of Greek fire.

Consequences

The defeat drained Umayyad resources and manpower at a time when the caliphate faced unrest elsewhere. Arab raids into Anatolia continued for decades, but no caliph again sent a full-scale expedition to take Constantinople. In 740 Leo III won a further victory over an Arab army at Akroinon in Anatolia.

Leo founded the Isaurian (or Syrian) dynasty and stabilised the empire. His reign is also remembered for the beginning of the controversy over religious images (see Byzantine Iconoclasm). Many historians argue that the victory of 718 protected south-eastern Europe from conquest for over 700 years, until the Ottomans took the city in 1453.

Timeline

• 717, 25 March: Leo III is crowned emperor in Constantinople.
• 717, summer: Maslama crosses the Hellespont at Abydos.
• 717, mid-August: The Arab army begins the siege of the land walls.
• 717, early September: Greek fire strikes the Arab fleet in the Bosporus.
• 717, September: Caliph Sulayman dies; Umar II succeeds.
• 717–718, winter: Severe cold, famine and disease in the Arab camp.
• 718, spring: Arab reinforcement fleets are destroyed; Bulgars attack in Thrace.
• 718, 15 August: The Arab army withdraws.

Why it matters

The failure of the siege of 717–718 halted the Umayyad advance in the East and ensured Byzantium’s survival as a Christian state. It marked a turning point in the long struggle between the caliphate and the empire and shaped the political and religious map of Europe and the Middle East.