Theodosian Walls (413): The Land Walls of Constantinople

The Theodosian Walls are the great land walls of Constantinople, built around AD 408–413 under the emperor Theodosius II and rebuilt after a devastating earthquake in 447. Stretching about 5.7 kilometres from the Sea of Marmara to the Golden Horn, their triple line of moat, outer wall and inner wall made the Byzantine capital one of the most strongly defended cities in history. For more than a thousand years they kept out almost every attacker, until Ottoman cannon breached them in 1453.

Why new walls were needed

When Constantine founded his new capital in 324–330 (see Founding of Constantinople), he built a wall across the peninsula about 2.8 kilometres west of the old Greek city of Byzantium. Within a century the population had outgrown it, with suburbs spreading beyond the gates.

The early 5th century was also a time of danger. Goths had defeated a Roman army at Adrianople in 378 and roamed the Balkans in the following decades, and the Huns were pressing on the Danube. Constantinople, protected by the sea on three sides, could be approached by land only from the west.

Building the walls, c. 408–413

Theodosius II became sole emperor in May 408 at the age of seven. Government was led by the praetorian prefect Anthemius, and it was under his direction that a new wall was begun about 1.5 kilometres west of Constantine’s line. A law of 413 preserved in the Theodosian Code refers to the towers of the new wall as complete, which gives the usual date for its completion.

The new line roughly doubled the area of the city. It enclosed large open cisterns, monasteries and gardens, which proved invaluable during long sieges.

The earthquake of 447 and the Huns

In January 447 a severe earthquake struck Constantinople and brought down large parts of the wall, including many towers. At the same moment Attila’s Huns were invading the Balkans.

The praetorian prefect Flavius Constantinus organised the rebuilding. He mobilised the citizens through the Blues and Greens, the chariot-racing factions of the Hippodrome, which also acted as large civic associations. According to inscriptions in Greek and Latin that still survive at the Mevlevihane Gate, the work was completed in less than two months.

At this time, or soon afterwards, the defences were greatly strengthened by the addition of an outer wall and a broad moat in front of the original structure. The result was the triple barrier that later visitors described with awe.

How the walls worked

From the outside in, an attacker faced:

• The moat: about 20 metres wide and up to 7 metres deep, divided by dams into sections that could be flooded, and lined with a low battlemented wall.
• The outer terrace: a strip of ground between the moat and the outer wall.
• The outer wall: about 2 metres thick and up to 8.5–9 metres high, with smaller towers placed between those of the inner wall.
• The inner terrace (peribolos): about 15–20 metres wide, where defenders could gather.
• The inner wall: the main barrier, about 5 metres thick and 12 metres high, with 96 large towers up to about 20 metres high.

The towers of the two walls were staggered so that those behind could fire over the gaps in front. Their builders used a core of mortared rubble faced with cut limestone blocks and bands of red brick, a technique that gave strength and some flexibility in earthquakes.

Gates alternated between public gates, with bridges across the moat, and military gates used only by the army. The most famous was the Golden Gate near the Marmara shore, a ceremonial arch used for triumphal entries; whether it was built under Theodosius I or Theodosius II is still debated.

A thousand years of sieges

The walls were tested again and again:

• In 626 the Avars and Persians besieged the city together while the emperor Heraclius was away (see Siege of Constantinople, 626).
• Arab forces of the Umayyad Caliphate threatened the city in the 670s and besieged it by land and sea in 717–718 (see Arab Siege of Constantinople).
• Bulgar rulers such as Krum in 813 and Simeon in the early 10th century reached the walls but could not break through them.
• In 1204 the Fourth Crusade captured the city by assaulting the weaker sea walls along the Golden Horn, not the land walls.

The final test came in 1453. The Ottoman sultan Mehmed II brought large bronze cannon that battered the walls for weeks. On 29 May 1453 his troops broke in near the Gate of St Romanus, in the low central section of the walls, and the city fell (see Fall of Constantinople).

The sea walls

The land walls were only part of the system. Single walls also ran along the Sea of Marmara and the Golden Horn, and these were joined to the Theodosian line at both ends. They were less massive because strong currents and the shoreline made assaults from ships difficult, and in wartime a chain could be stretched across the mouth of the Golden Horn to keep enemy fleets out.

Maintaining the defences

The walls were never finished in the sense of being left alone. Earthquakes struck Constantinople regularly, and emperors repaired the towers and curtains many times. Inscriptions naming emperors such as Leo III, Basil II and John VIII Palaiologos record work carried out over the centuries.

In the 7th and 12th centuries new walls were added at the northern end, around the Blachernae palace near the Golden Horn, where the Theodosian line met the sea. This section, without a moat because of the steep ground, was considered a weak point, and attackers often concentrated there.

Defence also depended on people. The walls were so long that the city needed many thousands of soldiers and armed citizens to man them fully. In 1453 the defenders numbered only about 7,000 to 8,000, far too few to hold both walls along the entire length, and they chose to fight from the outer wall.

The walls today

The Ottomans repaired the walls and used the Golden Gate area as part of the Yedikule (“Seven Towers”) fortress, which served as a treasury and prison. Over the following centuries the walls lost their military role, and market gardens grew in the moat.

Most of the circuit still stands. Since 1985 it has been part of the UNESCO World Heritage Site Historic Areas of Istanbul. Restoration work from the 1980s onward has been controversial, as some sections were rebuilt with modern materials that critics argue damaged the original fabric.

By the numbers

Timeline

• 330: Constantinople inaugurated with Constantine’s wall.
• 408, May: Theodosius II becomes sole emperor; Anthemius leads the government.
• 413: The new land wall is complete.
• 447, January: Earthquake damages the walls; they are rebuilt within two months.
• 626: Avar and Persian siege fails.
• 717–718: Arab siege fails.
• 1204: Crusaders take the city through the sea walls.
• 1453, 29 May: Ottomans break through the land walls.
• 1985: Walls inscribed on the UNESCO World Heritage List.

Why it matters

The Theodosian Walls were among the most successful fortifications ever built. By protecting Constantinople for over a thousand years, they allowed the Eastern Roman Empire to survive long after the West fell, preserving Roman law, Greek learning and Orthodox Christianity through the Middle Ages.