The Theodosian Walls

Reconstruction of the Theodosian walls in their Byzantine prime


The walls of Constantinople were the most impressive fortifications of any metropolis from antiquity or the medieval period, with its defenses playing a crucial role in the Arab sieges, and indeed any siege of Constantinople. This was not a place you wanted to attack! It is not without justification that these walls are so famous. These walls on more than one occasion were the difference between the fall and survival of the Roman Empire in the Middle Ages. I cannot think of any construction so crucial in Roman history. Eric McGreer made a good point that “the alluring wealth and prestige of Constantinople necessitated the construction and maintenance of fortifications capable of resisting assault.” Being one of the largest wealthiest cities automatically made Constantinople among the greatest potential sources of plunder. The medieval Romans believed that Constantinople was “guarded by God.” But as James Crow put it, also “possessed the most elaborate and complex urban fortifications in the ancient world, thanks to the legacy of Theodosius I and his successors.”


Source: The Byzantine Legacy. The inscription is translated as “O Christ, God, preserve Thy city undisturbed, and free from war. Conquer the wrath of the enemies.” The Byzantines did not trust only the fortifications and wanted divine protection.

The Theodosian walls have an amazing track record of success for the defense of Constantinople. The Theodosian walls proper, were never truly breached until 1453 by the Turks, who had the benefit of cannons and a much weaker Byzantine Empire to defend the city against them. Many opponents who may have attempted to besiege Constantinople had its fortifications been less formidable never even tried, and those who did did not see much success. For example, the Avars and Bulgars both dominated the Balkans at various times in Byzantine history. There were periods where outside of the walls of Thessaloniki and Constantinople, there was no truly safe place for the Romans. However, in most cases, these opponents did not even try to seriously besiege the city, and just raided the suburbs. The Avars attempted a siege in 626, with Persian support, however since neither of the two powers had a serious navy the siege was doomed to fail. The Bulgars never had a serious siege of Constantinople which was actually going to have a chance of taking the Roman capital. In 1204 when the city infamously fell after the Fourth Crusade attacked the city, the true weakness had been Blachernae and the Golden Horn sea walls. The Crusaders were wise enough not to focus on the Theodosian sections of the land wall, and the key to success was the powerful Venetian fleet.


The geography of the city made these walls possible. Surrounding an entire city in a circle with such a vast construction would have been far more challenging, and required much more manpower to defend. But the land approach was only the the western side, giving the defenders a huge advantage.

The city of Constantinople was not a city which could just be built anywhere, the unique geography of the Queen of Cities was crucial. Not only did it make Constantinople (and modern Istanbul) a beautiful city, the geography also helped protect the city. Constantine’s “New Rome” was surrounded by water on three sides, meaning that an approaching army could only attack the western and most formidable sections of the walls, the Theodosian walls. The infamous and impassable triple walls.

McGreer strongly emphasizes that an enemy had to attack both “by land and sea. The latter posed the lesser threat, since the prevailing winds and currents, not to mention the adverse conditions and winter storms that restricted the sailing season, worked against enemy vessels attacking the city from the Bosporos or the Sea of Marmora or attempting to maintain a blockade long enough to starve out the defenders. It was also no easy task to coordinate land and sea forces operating from the European and Asian sides of the Bosporos. As long as the enemy could be kept out of the Golden Horn, the city was relatively secure on its seaward sides. It was on the western, landward side where no natural obstacle impeded invaders that the city was susceptible to attack.” For this reason the Theodosian walls were constructed, and they did their job better than could have ever been expected.

McGreer added that “once enclosed by a circuit of walls, Byzantine Constantinople might best be pictured as an impenetrable island fortress which in a pre-gunpowder age could be taken only through the negligence or connivance of the city’s inhabitants.” This is why the Byzantines used a chain to block the Golden Horn, because the vulnerable point was the sea walls along the Golden Horn. The harbor was sheltered from the currents, and thus attacking ships could set up with ladders or other boarding mechanisms and launch attacks on the walls. This is how the Crusaders took the city in Constantinople, they broke the chain and attacked the weak point of the defensive “island.”


Constantine laying the course of the new walls of Constantinople, with Byzantium in the background. I saw this credited to Roger Payne on an image search.

The original walls of the city built by Constantine do not exist, and are not as well known, but clearly it was felt they were not overly impressive. Not to say they were terrible fortifications, the Constantinian wall did hold out against the Goths who had annihilated the Roman army at the Battle of Adrianople in 378AD, who tried to follow up their victory with a siege of Constantinople unsuccessfully. The wall probably was immediately no longer a priority to upkeep as soon as the new walls were built, but it was attested as standing in the 8th century, and a section was noted to collapse in 860AD. Thus, in some condition, it must have been standing even in the 9th century. Certain gates of the city were standing even in Ottoman times. Isa Kapi Mosque (The Gate of Jesus Mosque) is an approximate marker of where the ruins of the Golden Gate of the Constantinian walls stood during Ottoman times, and thus also during Byzantine times.


The new defenses were massive, stretching 6 kilometers from the Sea of Marmara to the Golden Horn. One of the things that is very important about the Theodosian walls is that they were built at a time when the Roman Empire was the preeminent power in this area of the world. This was not a project that any state could undertake at will. The Romans, even with the Empire split in two units, had a powerful economy and a huge population paying taxes and engaging in relatively stable and prosperous trade. The amount of laborers that worked on the Theodosian walls must have been staggering. To put it in context, the 9th century Byzantines had to get 6,000 men just to repair the Aqueduct of Valens and get it functioning again after it had laid dormant for a long time. For the medieval Romans, that was quite an achievement, but in Late Antiquity that was probably much more common and also exceeded for many projects. Even the Western Roman Empire could not afford such an undertaking most likely, it was the wealth of the Eastern Mediterranean that financed this grand construction. To give another example, in 447, it took 16,000 men from the Blues and Green (chariot racing factions) just to repair the walls. The Romans that came after Justinian would have struggled to pay for such a monumental set of fortifications, and the Theodosian walls saved the Empire from conquest when the Arabs besieged the capital in 717. Repairing them was a big undertaking for Byzantium, but one they undertook out of necessity. The walls turned out to be the most supreme inheritance from antiquity for the Byzantines. Thus, the choice to invest in these fortifications was the most important building project in Roman history. I cannot think of a more existentially crucial building project in history, in fact.


The name of the Theodosian walls is for the Emperor Theodosius II who reigned during their construction. Naturally any Emperor would take credit, and I suppose he was the man who paid the bills for the walls. In reality, the one who actually oversaw the construction of the walls was the Praetorian Prefect of the East, a man named Anthemios. Theodosius II was only 12 years old when the original line of the walls was completed. In the words of Turnbull Anthemius “applied himself with vigour to whatever task the Empire demanded of him. The first task was the expulsion of the Huns from the Balkans. The second resulted in the walls of Constantinople…the so-called Theodosian walls were the results of Anthemius’ skilled and dedicated work. His walls were to set in stone the limits that Constantinople was to possess and to defend until modern times. Today, tourists to Istanbul can find Anthemius’ limits marked on the map as the ‘Old City’…the Theodosian walls defined what for the next 1500 years was to be understood as Constantinople.” Definitely if one is thinking of the Theodosian walls, Anthemius deserves his credit and honor for such a magnificent work!


As the New Rome grew, the city needed an expansion. Stephen Turnbull describes how “the growing population could not forever be housed conveniently within the confines of Constantine’s original city plan.” The city was already spilling out into suburbs which were vulnerable outside the city walls, and the Roman world was getting increasingly insecure. First, there was a triumphal arch now known as the Golden Gate, which was clearly built earlier, in 390AD. This raises questions as to whether that was the beginning of the project or just something incorporated into the new walls. Cyril Mango wrote that: “It seems obvious to me that the gate, with its massive pylons, was planned in the context of the new land walls, which for all I know, may have been on the drawing board already in the time of Theodosius (the Great).” There is evidence the walls were being constructed during the successor of the Theodosius I in the East, his son Arcadius. The dates of construction of what Eric McGreer rightly describes as “the most imposing and complex defenses guarding any city in the Roman world” are generally given as 405-413 for the main two walls. The main wall is the tallest wall, the large rear wall of the triple walls. The second wall is the wall in front of that, still a respectable wall. And in front of that, a third small wall which also served to as a retaining wall for the moat. The third wall was not added until 447. Though other cities had double walls, according to James Crow “it is clear that their construction was an entirely novel response to the requirements of the new capital.” The scale of the walls was unlike anything else, and a unique aspect was that the ground in between the two larger walls was higher than the ground around it. The walls were thus extra high.

This is featured in the book The Fall of Constantinople: The Ottoman Conquest of Byzantium, which is mentioned in the sources at the bottom of the article. The original walls of Anthemius were the inner and outer wall, you can see the raised ground between them.

This move shifted the western boundary of the city 2 kilometers west of the walls of Constantine. A 6.5 kilometer was a gargantuan project, and to get it done in eight years must have required a numerous horde of workers. Not to mention that work was also going on around the seaside perimeter of the city, though the sea walls would not be finished until 439. The course of the walls seem to have been dictated by pragmatic urban concerns. The food and water supply, always the lifeblood of a metropolis, were ever the concern for the imperial administration. There were three large cisterns which were outside the walls of Constantine, which were incorporated in the Constantinople 2.0 that the Theodosian walls created. The large space between the walls was not ever entirely filled with urban landscape, and gave the city space for agriculture, animals, storage, cisterns, and other things which added new assets to Constantinople.


The population of the city itself had to make sacrifices for this new security-guarantee. But, considering Rome was sacked in 410AD, it was a good investment. It is hard not to think that the Eastern Romans, seeing Rome sacked a second time by the Vandals in 455, did not look at their walls and see the immense value of what they had paid for. Turnbull explained the obligations of the citizenry: “From the moment that Anthemius’ designs began to take shape the erection, maintenance and repair of the new fortifications of the city became an undertaking in which all citizens were required to assist in one form or another. On that point, laws were very strict, and neither rank not privilege exempted anyone from their obligation to carry out the work. One-third of the annual land tax of the city went towards the cost of the walls, and any additional expenditure was provided by requisitions laid upon the inhabitants. There does not seem to have been much grumbling about the matter. Indeed, there was a genuine enthusiasm for a project that promised increased security, and the government harnessed such enthusiasm in various ways. One subtle ploy was the way the government appealed to the citizens’ generosity through the circus factions, chariot-racing teams, such as the Blues or the Greens, that they supported. The supporters were great rivals when cheering on their side from the terraces of the Hippodrome, but worked together on the walls when the city was threatened. Records show that in 447, when repairs were being undertaken, the Blues and Greens supplied 16,000 men between them for the building effort.” As security was decreasing for the people of the Roman Empire, who would not want to make some sacrifices for the best protection possible?


In 447AD, when the fabled walls were still young and relatively new, a disaster struck. Geology is one thing that the walls still were not strong enough for, and when a powerful earthquake shook the earth of Constantinople huge sections of the Theodosian walls crumbled just 34 years after being completed. 447 was not an ideal time geopolitically, not just geologically, for the city of Constantinople. Attila the Hun was in the Balkans, this was a dire threat. However, the people of Constantinople came to the rescue. The above mentioned 16,000 men from the circus factions were provided, among surely others including soldiers and other able-bodied men, who all came together to save their city. Turnbull describes the heroic efforts: “Fortunately, in a splendid confirmation of the energy and commitment to their defence that the citizens of Constantinople had shown before, the government and people rose to the challenge and restored the fallen walls in less than three months. These new walls helped save Constantinople from Attila, although some sources tell of an epidemic among his followers.” Eric McGreer says that there are inscriptions which are “boasting that the reconstruction had taken just sixty days, ‘an achievement even Pallas Athene could scarcely have matched.'”

There is no Anthemius here, we do not know much about the identity of whoever was in charge of the emergency restoration project. It was possibly a man named either Constantine or Cyrus. This is when the Theodosian walls took on their final form. Turnbull wrote that “our anonymous hero went much further than mere restoration, and took the opportunity to make the city into a much stronger fortress even than Anthemius had dared to contemplate. An extra wall was built outside Anthemius’ wall, with a broad and deep moat in front of it. When the work was complete, the city lay behind three lines of defence and 192 towers flanked the walls. It was these walls that were to prove impregnable for the next 1,000 years and still survive to this day.”

I cannot even imagine how, at least before gunpowder, anyone could even seriously attempt to attack these walls. Attila the Hun probably decided that there was much easier plunder to take than trying to hopelessly attack these walls.

Attila the Hun could not attack Constantinople with these walls, even without an epidemic. Without a fleet he could not blockade the city and his horse-archer army could not be used properly to full effect. If he had tried, I cannot see any way he succeeded in taking the city after the repairs and upgraded were in effect. After 447, fortress Constantinople was complete with the triple walls, and the sea walls which had been completed in 439. The walls would go on to help the Romans survive crises much more dire than just Attila being in the area in future centuries, essentially making Constantinople the only refuge the Romans had at times.


(Photo Credit: The Byzantine Legacy) These are the walls built by Herakleios and Leo V

The Theodosian walls are pretty uniformly constructed, but if you follow the walls from the Marmara to the Golden Horn, at some point towards the North you will find a radical change in the construction of the walls. These are the walls of Blachernae. Turnbull notes that “even the most cursory visitors cannot help but notice that towards the northern extremity of the walls there is a change in design. Just before they head downhill towards the Golden Horn, the Theodosian walls come to an abrupt end and are replaced by a wall of more complex and different construction. This is something of a puzzle. Surely the Theodosian walls originally extended all the way to the Golden Horn, so why were they replaced?”

It is indeed rather odd to me personally, that there was a perfect line of defenses, and yet the Byzantines, even during tough times, decided to weaken those defenses to prioritize other concerns. In 627 during the rule of Emperor Herakleios, the Blachernae area was still just a suburb outside the Theodosian walls. In this suburb was the Church of the Theotokos, and it was believed to have divine protection. The Church had a holy spring inside of it. Also, in 626, the icon known as the Blachernitissa, was paraded along the walls of Constantinople and believed to possess a great deal of holy power. The Romans decided that the Church should be inside the city, and that it would help the city be safer with divine protection. Herakleios added another wall to expand the city there. I assume that material was taken from the Theodosian walls for this purpose, as the Empire was in the last stage of a long costly and existential total war against the Persians in 627. In 813 Emperor V upgraded the walls to protect against the Bulgars. And during the Komnenian era, the walls were extensively modified as Blachernae had become the imperial residence. There is a still a wall known as the wall of Manuel Komnenos, which was a second wall covering part of the Blachernae area which offered extra protection to the imperial residence, the Blachernae Palace. According to Alexander van Millengen the wall built by Manuel “was not only stronger than earlier defenses of the palace, but had also the advantage of removing the point of attack against this part of the city to a greater distance from the Imperial residence. At the same time, the older fortifications were allowed to remain as a second line of defence.”


The materials used to construct the wall were square blocks of stone, bricks, and limestone mortar. In some areas blocks of reused marble are incorporated into the construction of the walls as well. The materials were sources from quarries around the Marmara sea, which had an ample selection of stone materials to use for the Theodosian walls. The stone bricks in the wall were quarried nearby in a quarry just a few miles from the Golden Gate built by Theodosius. We are not sure exactly where the bricks were made, but it was likely in local kilns. The mortar mixture was created by mixing brick dust and tiny fragments of stone together with lime. This created an extremely strong mortar. The walls are constructed in the stereotypically Byzantine way, where they are alternating bands of bricks and stone together in an aesthetically pleasing and pragmatic fashion. The stone and bricks were on the outside, and inside was mortar-bound rubble which was in between the faces of the wall. The main inner wall of the Theodosian walls has 6 bands of brick, each 5 bricks tall. They are typically about one foot wide and 2 inches tall. Some of them are stamped, some are not.


David Nicolle, John Haldon, Stephen Turnbull. The Fall of Constantinople: The Ottoman Conquest of Byzantium (2007).

The Cambridge Companion to Constantinople, Edited by Sarah Bassett (2022). In particular, chapter 7 “The Defence of Constantinople” by Eric McGreer


Byzantine Constantinople: The Walls of the City and Adjoining Historical Sites by Alexander Van Millengen (1899)