The Walls of Constantinople

The land walls of Constantinople are the most successful fortification in history by the simple measure of how long they worked. Completed in the 410s and 440s, they were assaulted by Huns, Avars, Persians, Arabs, Bulgars, Rus, Pechenegs, Crusaders and Ottomans, and were not breached by direct assault until 1453 — a working life of over a thousand years. The one earlier capture, in 1204, came through the sea walls on the Golden Horn, which were much weaker.

Something like six and a half kilometres of them still stand, in varying condition, cutting across the Istanbul peninsula from the Sea of Marmara to the Golden Horn. They are among the very few pieces of Byzantine military architecture that can be walked from end to end.

The First Walls

The Greek colony of Byzantion had its own walls, and Septimius Severus rebuilt them after sacking the city in 196. When Constantine founded his new capital, he built a new line about two and a half kilometres west of the old circuit, enclosing an area several times larger. Almost nothing of the Constantinian wall survives; its line is known approximately from written sources.

Within eighty years the city had outgrown it.

The Theodosian Land Walls

The Wall of 413

In 413, during the minority of Theodosius II, the praetorian prefect Anthemius built a new wall roughly a mile and a half west of Constantine’s, enclosing the growing suburbs. This is the inner wall of the system as it survives: about five metres thick and twelve metres high, with ninety-six towers at intervals of around fifty-five metres, each rising some five metres above the curtain.

The construction is characteristically late Roman: a core of mortared rubble faced with squared limestone blocks, bonded at intervals by courses of brick running through the full thickness of the wall. The brick courses are not decoration; they tie the facing to the core and give the structure a degree of flexibility, which is one reason it has survived a great many earthquakes.

The Earthquake of 447 and the Outer Defences

In 447 a severe earthquake brought down a long stretch of the wall and many towers, at the moment when Attila’s Huns were in the Balkans. The repair, carried out under the prefect Constantine in what the sources describe as sixty days, using the circus factions as an organised labour force, did more than restore the original: it added an outer wall and a moat, converting a single barrier into a defence in depth.

The resulting system, from the attacker’s side inward, was:

Element	Dimensions (approximate)
Moat	20 m wide, 7 m deep, brick-lined, with a low breastwork
Outer terrace (parateichion)	15–20 m wide
Outer wall	2 m thick, 8–9 m high, with 96 towers
Inner terrace	15–20 m wide
Inner wall	5 m thick, 12 m high, with 96 towers up to 20 m high

The towers of the two walls were deliberately staggered so that the inner towers commanded the gaps between the outer. An attacker who carried the moat faced a second obstacle under fire from above and behind; an attacker who carried the outer wall found himself in a killing ground overlooked by the inner towers.

Whether the moat was normally filled with water is disputed; there is no clear evidence of a supply system, and it may have been a dry ditch, which would have served nearly as well.

The Sea Walls

The land walls were only part of the circuit. Sea walls ran along the Marmara shore and the Golden Horn, about eight and a half kilometres in total, mostly single-line and much lower — the sea itself, the currents of the Bosphorus and the chain across the Golden Horn were considered sufficient additional defence.

The chain is worth its own note: a heavy iron boom on wooden floats, drawn across the mouth of the Golden Horn from a tower at the Acropolis to the Galata side, capable of stopping a fleet. It worked repeatedly. It failed in 1204 when the Venetians broke it, and was bypassed in 1453 when Mehmed II had ships dragged overland on greased rollers into the Horn.

The Gates

The wall had a number of public gates and smaller military posterns. The most important were:

• The Golden Gate — a triumphal arch of the late fourth century incorporated into the wall, with three arches and, originally, gilded doors and a bronze quadriga. Imperial triumphs entered here and processed along the Mese to the palace. It survives, walled up, inside the Ottoman fortress of Yedikule.
• The Gate of St Romanos — the Pempton sector nearby, where the Lycus stream crossed the line, was the weakest point, since the ground dips and attackers could approach on the level. Every serious besieger concentrated here, and so did the fighting in 1453.
• The Kerkoporta — a small postern which, according to the historian Doukas, was left unbarred on the morning of 29 May 1453 and let the first Ottoman troops inside.

What the Walls Withstood

• 626 — the Avar and Persian siege, with the emperor absent in the Caucasus
• 674–678 and 717–718 — the two great Arab attempts
• 813 and 913 — Bulgar armies under Krum and Simeon, both of which looked at the walls and negotiated instead
• 860, 941, 1043 — Rus fleets, defeated at sea
• 1090s — Pechenegs
• 1422 — a full Ottoman siege under Murad II, abandoned

The pattern is consistent: besiegers who could not starve the city out, because the sea remained open, eventually went away.

Maintenance

A fortification of this size required continuous work, and the Byzantines took it seriously. Inscriptions on the towers record repairs by emperors from the fifth century to the fifteenth — Leo III, Basil II, Michael VIII, John VIII — and the cost was met by a dedicated tax and by the labour obligations of the districts behind each sector. In the final years, when the treasury was empty, repairs were funded by public subscription, and the historian Doukas records bitterly that money collected for the walls had been hoarded rather than spent.

1453: Why They Failed

The walls were not defeated by a new tactic. They were defeated by artillery and arithmetic.

Mehmed II brought a siege train including very large bombards — the largest, cast by the Hungarian founder Orban, is described as needing sixty oxen to move and taking hours to reload. These guns could not be aimed precisely and were dangerous to their crews, but over fifty-four days of bombardment they brought down stretches of the outer wall faster than the defenders could rebuild them.

The arithmetic mattered as much. The circuit required something like twenty thousand men to hold properly. Constantine XI had between seven and eight thousand, including the Genoese under Giustiniani. A wall is a force multiplier, not a substitute for a garrison; at that ratio, a determined attacker who can maintain pressure at several points will eventually find the line thin somewhere. The full account is in the fall of Constantinople.

The Walls Today

Long stretches survive along the line of Sultan Süleyman and Adnan Menderes avenues, including well-preserved sections near Yedikule, Belgradkapı and Silivrikapı, and the Blachernae section at the northern end where the wall changes character entirely — a single, much higher wall of the eleventh and twelfth centuries protecting the palace quarter.

Restoration since the 1980s has been controversial. Some sections have been rebuilt in modern brick and concrete with insufficient archaeological control, and the results have been criticised by UNESCO, which lists the walls as part of the Historic Areas of Istanbul world heritage site. Earthquake risk, encroachment and the sheer length of the monument make conservation difficult. Anyone walking the line today sees, in a few kilometres, both fifth-century masonry that has stood for sixteen centuries and 1990s repairs already failing.

Building and Paying for Them

A fortification of this scale is a permanent fiscal commitment, and the Byzantines organised one.

Construction and repair were funded by a dedicated tax and by the labour obligations of the districts behind each sector. The circus factions supplied organised manpower — the rebuilding after the earthquake of 447 was carried out by faction labour under the prefect Constantine, and an inscription recording the work survives.

Sectors were assigned. The demes, the guilds and the monasteries each had a stretch to man and maintain, and this allocation persisted for a thousand years; the defence of 1453 was organised on the same principle, with named commanders responsible for named sections.

Repairs are recorded in inscriptions on the towers from the fifth century to the fifteenth, naming emperors from Theodosius II to John VIII. Reading the towers in sequence is a way of reading the empire’s fiscal history: dense imperial inscriptions in the prosperous centuries, and in the last decades a note that a section was repaired from money collected by public subscription.

The Blachernae Sector

The northern end of the land walls is a different structure and is frequently misdescribed.

When the Blachernae quarter, with its shrine of the Virgin, was brought inside the defences, the line there was rebuilt as a single wall of much greater height — around twelve to fifteen metres — with closely spaced towers and no moat, since the ground falls away steeply.

From the eleventh and twelfth centuries this became the imperial quarter: the Komnenian and Palaiologan emperors moved their residence here from the decayed Great Palace, and the wall was strengthened accordingly. The Palace of the Porphyrogenitus, the Tekfur Sarayı, stands in this section and is the only Byzantine palace building in Istanbul surviving to roof height.

The Blachernae sector’s weakness was that it lacked the triple depth of the Theodosian line. It was where the Fourth Crusade forced an entry in 1204, attacking from the Golden Horn, and where Ottoman troops broke in through the Kerkoporta postern in 1453.

What a Besieger Faced

Setting the obstacles out in sequence explains the record.

An attacker at the moat is under missile fire from the outer wall’s towers and, at longer range, from the inner wall’s higher towers behind them. Crossing the moat under that fire, he reaches a low breastwork, then the outer terrace, then a wall eight or nine metres high.

Carrying the outer wall puts him on a narrow terrace fifteen to twenty metres wide, overlooked by the inner wall twelve metres high with towers rising to twenty — a confined killing ground with no cover, which the defenders can enfilade from the staggered towers on both sides.

Siege towers must be built tall enough to overtop the inner wall and then moved across a filled moat and a captured outer line, on ground that has been deliberately kept clear. Mining is defeated by the rock beneath. Ramming requires reaching the wall foot.

No pre-gunpowder army solved this problem. The walls were not defeated by better siegecraft; they were defeated by artillery and by a garrison a third the size it needed to be.

• Constantine the Great and the Founding of Constantinople — the first circuit
• The Fall of Constantinople — the siege that ended their record
• The Siege of Constantinople, 717–718 — the greatest test they passed
• The Avar Siege of 626 — the walls held with the army away
• The Byzantine Army — the garrison that manned them
• The Fourth Crusade — the breach that came from the water
• Constantinople to Istanbul — the city inside them after 1453