Who Built the Theodosian Walls of Constantinople?

The Theodosian Walls were an impenetrable defense system built by Emperor Theodosius II to protect the city of Constantinople.

Jul 14, 2023By Vedran Bileta, MA in Late Antique, Byzantine, and Early Modern History, BA in History

theodosian walls 3d feature


Built in the early fifth century CE by the orders of Emperor Theodosius II, the Theodosian Walls stood as the main line of defense, protecting Constantinople and the Eastern Roman Empire for over a millennium. Constructed under the supervision of Anthemius, the triple defensive system acted as a veritable bastion, defending approaches to the imperial capital by land. The walls withstood numerous sieges and repelled various invasions throughout Byzantine history. They also symbolized the power and resilience of the Medieval Roman Empire. Finally, in 1453, the walls of Theodosius finally succumbed to the relentless assault of the Ottoman cannons. The Walls, and the city they defended for a thousand years, fell, marking the end of the Roman Empire and the advent of the gunpowder age. 


Emperor Theodosius II Built the Theodosian Walls

theodosian walls restored section
The restored section of the Theodosian Walls, built in the early fifth century CE, to protect the city of Constantinople by attack from the mainland, author’s personal collection


The Theodosian Walls were not the first walls of Constantinople, the capital of the Roman Empire (also known as the Byzantine Empire). When emperor Constantine the Great founded Constantinople in 330 AD, he chose the optimal location for his new city. Situated on an easily defensible peninsula at the crossroads of Europe and Asia, Constantinople held immense strategic importance. To secure approaches to the city by land, the emperor ordered the construction of so-called Constantinian walls. However, following the Danubian limes’ collapse and a disaster at Adrianople in 378, it became apparent that the city needed a much stronger defensive perimeter. The solution was a triple defensive system – the Theodosian Walls – named after the emperor Theodosius II, who ordered the construction of the massive fortifications.


The Role of Anthemius in Building the Walls

theodosian walls Constantinople reconstruction
Reconstruction of the Theodosian walls of Constantinople


Emperor Theodosius II gave his name to the walls, but most of the work was done under the supervision of Flavius Anthemius, the praetorian prefect of the East, who practically ruled the Empire in the boy-emperor’s name. By the fifth century, Constantinople was expanding rapidly, outgrowing the boundaries marked by the Constantinian wall. To protect the city, Anthemius initiated the construction of the new wall, located about 1500 meters west from the old one. The new wall also had to adapt to the rapidly changing political and military situation, as by then, the Huns threatened the Eastern Roman Empire. Completed in 413 AD, after almost ten year of construction, the extended new wall nearly doubled the size of the city, making Anthemius, essentially, “the second founder of Constantinople.”


The Theodosian Walls Were an Unconquerable Stronghold

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The cross-section showing the triple defenses of the Theodosian Walls

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Built in two phases during the reign of Theodosius II (402 – 450), the Theodosian Walls were an impregnable bastion. The walls, measuring around six kilometres in length, consisted of three lines of defense. The would-be conqueror had first to cross the wide moat (filled with water), protected by the low wall, 1.5 meters tall. Next, the invader would have to cross the open ground before reaching the outer wall, 8-9 meters in height. The last and most powerful line of defense was the massive inner wall, 12 meters high and almost 5 meters thick. To make life more difficult for would-be conqueror, the Theodosian walls were bolstered with more than 90 towers, which held the artillery engines. No wonder, no invader managed to breach the walls for a thousand years.


The Walls Were Constantly Maintained, Repaired and Upgraded

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Reconstruction of the majestic Golden Gates, the main entry through the Theodosian Walls in peacetime


When completed, the Theodosian Walls were a sight to behold. A powerful triple defensive system, dominated the approach to the city by land. Strategically positioned towers and gates adorned the walls, allowing controlled access in times of peace while ensuring extra protection during the siege. The most imposing gateway, the monumental Golden Gates, was used for various imperial ceremonies and processions, serving as a starting point for the main avenue – the Mese – leading to the heart of the imperial capital – Hagia Sophia and the Great Palace. The walls had to be constantly maintained, repaired and upgraded. The most significant extension was undertaken in the eleventh century, during the reign of the Komnenian emperors, who ordered the construction of a whole new section to protect the Blachernae Palace near the Golden Horn.


Constantinople’s Most Important Defense

Constantinople sea walls hippodrome aerial view
Constantinople and its sea walls, with the Hippodrome, Great Palace, and Hagia Sophia in the distance, ca. 10th century, by Antoine Helbert


The Theodosian Walls were Constantinople’s most important line of defense. But they were not the only barrier protecting the city. The Sea Walls protected the imperial capital from naval attack and offered additional protection to the ships moored in the city’s principal harbor’s on the Sea of Marmara. Lastly, in the early sixth century, emperor Anastasius ordered construction of another additional defensive perimeter, in Constantinople’s hinterland. Located 60 km from the capital, and its Theodosian Walls, the Anastasian Wall, also known as the Long Wall of Thrace, enclosed the entire peninsula, providing the first line of defense. However, the 56-kilometers long walls were difficult to defend, buying time for Constantinople’s garrison to prepare for the siege.


The Theodosian Walls Were Breached Only Once

topkapi gate of st romanus
The Topkapi gate, known by the Byzantines as the Gate of St. Romanus, where the cannons of Mehmed II cracked the Theodosian Walls in 1453, author’s private collection


Soon after their construction, the Theodosian Walls were severely damaged by the first of many earthquakes that hit Constantinople in its long history. Yet, they were repaired in the nick of time, preventing the invaders, led by Attila the Hun, from taking the city. Instead, the Huns redirected their efforts toward the Western Roman Empire, where they clashed with the Roman general Aetius in the Battle of Chalons in 451 AD. The imposing Theodosian Walls would remain an impregnable obstacle for any invader who dared to take the city in the following centuries. Only in 1453 would the Ottomans manage to take breach the walls with the help of a new invention – the cannon. The fall of the ancient bastion, which defended the city and the Byzantine Empire for a millennium, led to the fall of Constantinople, ushering in a new age – the age of gunpowder. 

Yet, long after the Empire left the stage of history, the Theodosian Walls still stand in the center of modern Istanbul, as a silent witness to the vanished empire, a powerful symbol of its glorious past.

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By Vedran BiletaMA in Late Antique, Byzantine, and Early Modern History, BA in HistoryVedran is a doctoral researcher, based in Budapest. His main interest is Ancient History, in particular the Late Roman period. When not spending time with the military elites of the Late Roman West, he is sharing his passion for history with those willing to listen. In his free time, Vedran is wargaming and discussing Star Trek.