The Walls of Constantinople are a series of stone walls that have surrounded and protected the city of Constantinople (today Istanbul in Turkey) since its founding as the capital of the Eastern Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of Antiquity, and one of the most complex and elaborate systems ever built.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, when well manned, they were almost impregnable for any medieval besieger, saving the city, and the Byzantine Empire with it, during sieges from the Avars, Arabs, Rus', and Bulgars, among others (see Sieges of Constantinople). The advent of gunpowder siege cannons rendered the fortifications less impregnable, although the end of the final siege, leading to the fall of Constantinople to the Ottomans on May 29th 1453, seems to have come about because some Ottoman troops gained entrance through a gateway, rather than because the walls had been broken down.
The walls were largely maintained intact during most of the Ottoman period, until sections began to be dismantled in the 19th century, as the city outgrew its medieval boundaries. Despite the subsequent lack of maintenance, many parts of the walls survived and are still standing today. A large-scale restoration programme has been under way since the 1980s, which allows the visitor to appreciate their original appearance.
The original fortifications of the city were built in the 7th century BC, when it was founded as Byzantium by Greek colonists from Megara, led by the eponymous Byzas. At the time the city consisted of an acropolis and little more. Byzantium, despite being a prosperous trading post, was relatively unimportant during the Roman period, but featured prominently in the civil war between Septimius Severus and Pescennius Niger, holding out a Severan siege for three years (193-96 AD). As punishment, Severus had the strong walls demolished and the city deprived of its status. However, appreciating the city's strategic importance, he rebuilt and endowed the city with many monuments (including the Hippodrome) and a new set of walls, increasing its area. No details are known of the Severan Wall, except its general course and that its main gate was located shortly before the entrance of the later Forum of Constantine.
When Constantine the Great moved the capital of the Empire to Byzantium, which he refounded as Constantinopolis, "City of Constantine", he greatly expanded the new city by building a new wall about 2.8 km (15 stadia) westwards of the Severan wall and incorporating even more territory. Constantine's fortification consisted of a single wall, reinforced with towers at regular distances, which began to be constructed in 324 and was completed under Constantius II. The approximate course of the wall is known, running from the area of the Plateia Gate of the Golden Horn sea walls to near the Gate of St. Aemilianus on the Propontis walls (see section on the Sea Walls below). The wall survived during much of the Byzantine period, even though it was replaced by the Theodosian Walls as the city's primary defence; it still stood when Justinian ascended the throne, but only the Old Golden Gate, often attributed to Constantine but of uncertain age, still survived to late Byzantine times, until destroyed by an earthquake in 1509. The gate, known by chroniclers as the "Gate of Attalos", was described by the late Byzantine scholar Manuel Chrysoloras as being built of "wide marble blocks with a lofty opening", and crowned by a kind of stoa. In earlier centuries, it was decorated with many statues, including one of Constantine, which fell down in an earthquake in 740. In late Byzantine times, a painting of the Crucifixion was placed on the gate, leading to its Ottoman name, İsakapi ("Gate of Jesus").
Already by the early 5th century however, Constantinople had expanded outside the Constantinian Wall, in the extramural area known as the Exokionion.
In 408, during the reign of Emperor Theodosius II, construction began on a new wall, about 1,500 m to the west of the old, which stretched for 5,630 meters between the Sea of Marmara and the suburb of Blachernae near the Golden Horn. The new wall, which, despite the fact that construction commenced when the Emperor was seven years old, became known as the Theodosian Wall (Greek Theodosianon Teichos). The wall was built under the direction of Anthemius, the Praetorian prefect of the East, and completed in 413. The walls stretched for about 5.5 km from south to north, from the Marble Tower, Turkish Mermer Kule (in Greek Pyrgos Vasileiou kai Kōnstantinou, "Tower of Basil and Constantine") on the Propontis coast to the Blachernae, ending at about the area of the Palace of the Porphyrogenitus (known in Turkish as Tekfur Saray), where they adjoined the later walls of Blachernae. New Rome now enclosed seven hills and justified the appellation Eptalofos, like Old Rome. On November 6 447, however, a powerful earthquake destroyed large parts of the wall, and Theodosius II ordered the urban prefect Cyrus of Panopolis (sometimes referred to as Constantine) to supervise the urgent repairs, as the city was threatened at the time by Attila the Hun. Cyrus employed the city's dēmoi (more widely known as "Circus factions") in the work, and succeeded in restoring the walls within 60 days, as testified in two inscriptions in Greek and Latin on the Mevlevihane Gate. At the same time, a second outer wall was added, and a wide ditch opened in front of the walls.
The walls were built in two lines of defense, which adjoined the ditch. The main Inner Wall (Шаблон:Polytonic, Esō Teichos or Mega Teichos, "Great Wall") is a solid structure, 5 meters thick and 12 meters high. It is faced with carefully cut limestone blocks, while its core is filled with mortar made of lime and crushed bricks. Between seven and eleven bands of brick, ca. 40 cm thick, traverse the structure, not only as a form of decoration, but also strengthening the cohesion of the structure by bonding the stone façade with the mortar core, and increasing endurance to earthquakes. The wall was strengthened with 96 towers, mainly square but also octagonal or hexagonal, 18-20 meters tall, and placed at intervals of 55 meters. Each tower had a battlemented terrace on the top. Its interior was usually divided by a floor in two chambers. The lower chamber, which opened to the city, was used for storage, while the upper one could be entered from the wall's walkway, and had windows for view and for firing projectiles. Access to the wall was provided by large ramps along their side.
The Outer Wall (Шаблон:Polytonic, Exō Teichos or Proteichisma) was built 15–20 metres from the main wall, creating a space between the two walls called perivolos. The Outer Wall was 2 metres thick at its base, and featured arched chambers on the level of the perivolos, crowned with a battlemented walkway, reaching a height of 8.5 meters. Access to the Outer Wall from the city was provided either through the main gates or through small posterns on the base of the Inner Wall's towers. The Outer Wall likewise had 96 towers, square or crescent-shaped, situated midway between the Inner Wall's towers, and acting in supporting role to them. They featured a room with windows on the level of the perivolos, crowned by a battlemented terrace, while their lower portions were either solid or featured small posterns, which allowed access to the outer terrace. The Outer Wall was a formidable defensive edifice in its own right: in the sieges of 1422 and 1453, the Byzantines and their allies, being too few to hold the both lines of wall, concentrated on the defense of the Outer Wall.
The moat (souda) was situated at a distance of about 15 metres from the Outer Wall, creating a terrace called parateichion, where a paved road ran along the walls' length. The moat itself was about 20 metres wide and 10 metres deep, featuring a 1.5 metre tall crenellated wall on the inner side, serving as a first line of defence. Transverse walls in the moat allowed it to be flooded and retain water even though the walls followed the rise of the land.
The wall contained 8 main gates and a number of smaller posterns. The main public gates led across the moat on bridges, while the secondary gates, traditionally called "Military Gates", led to the outer sections of the walls. It must be noted however that this division is mostly a matter of historiographical convention, as there is sufficient evidence that several of the secondary gates were also used by civilian traffic, and indeed, the very accuracy of the division between civilian and "military" gates has been questioned.
The exact identification of several gates is a debatable, both because the Byzantine chroniclers provide more names than the number of the gates and because of the inadequate information provided by literary and archaeological sources. In order, from south to north, these gates were:
The Golden Gate (Ελληνικά. Χρυσεία Πύλη, Latina. Porta Aurea, Türkçe. Altınkapı or Yaldızlıkapı), was the main state entrance into the capital, used especially for the occasions of a triumphal return of victorious emperors from battle. The Gate was used for triumphal entries until the Komnenian period; thereafter, the only such occasion was the entry of Michael VIII Palaiologos into the city on 15 August 1261, after its reconquest from the Latins.
Originally, the Golden Gate was a triumphal arch, erected in ca. 388, during the reign of Theodosius I, to celebrate his victory over Magnus Maximus. At that time it stood alone, well outside the Constantinian Wall, straddling the Via Egnatia. It is architecturally elaborate, built of large square blocks of polished marble fitted together without cement, with three arches, and was decorated with numerous sculptures, including a bronze elephant-drawn quadriga on top, echoing the Porta Triumphalis of Rome. The gates themselves were originally plated in gold, whence their name derives. In 965 however, Nikephoros II Phokas installed the captured bronze city gates of Mopsuestia in their place.
When the gate was incorporated into the Theodosian Walls, an outer gate was added, which in later centuries was flanked by an ensemble of reused marble reliefs in two tiers. According to descriptions of English travelers from the 17th century, these reliefs featured mythological scenes. These reliefs, lost since the 17th century, were probably put in place in the 9th or 10th centuries to form the appearance of a triumphal gate. According to other descriptions, the outer gate was also topped by a statue of Victory, holding a crown.
After the Ottoman conquest, the Yedikule Fortress was erected behind the gate complex. Since the main Gates were usually kept closed, a small postern exists after the Fort (between towers 11 and 12), the so-called Yedikule Kapısı, which was used for everyday traffic. The Golden Gate was emulated by the Kievan Rus', who built monumental city gates named "Golden Gate" at Kiev and Vladimir.
The Second Military Gate or Xylokerkos Gate (Шаблон:Lang) lay between towers 22 and 23. Its second name derives from the fact that it led to a wooden circus (amphitheatre) outside the walls. Its is known today as Belgrade Gate (Belgrad Kapısı), after the Serbian artisans settled there by Sultan Suleyman the Magnificent after he conquered Belgrade in 1521. According to a story related by Niketas Choniates, in 1189 the gate was walled off by Emperor Isaac II Angelos, because according to a prophecy, it was this gate that Western Emperor Frederick Barbarossa would enter the city through. It was re-opened in 1346 but closed again before the siege of 1453, and remained closed until 1886.
The Gate of the Spring or Pēgē Gate (Шаблон:Lang) was named so after a monastery outside the Walls, the Zōodochos Pēgē ("Life-giving Spring") in the modern suburb of Balıklı. Also known as the Gate of Melantias (Porta Melantiados) because there the old highway from the town of Melantias entered the city, and is possibly the so-called Gate of Kalagros (Шаблон:Polytonic). In Turkish, it is known as the Selymbria Gate (Silivri Kapısı). It lies between towers 35 and 36, which were extensively rebuilt in later Byzantine times, while the gate arch itself was replaced in Ottoman times.
It was through this gate that the forces of the Empire of Nicaea, under General Alexios Strategopoulos entered and retook the city from the Latins on 25 July 1261.
This gate lies shortly after the Pege Gate, exactly before the C-shaped section of the walls known as the "Sigma", between towers 39 and 40. It has no Turkish name, and is of middle or late Byzantine construction. The corresponding opening in the outer wall preserved until the early 20th century, but has since disappeared.
The Gate of Rhegion (Шаблон:Polytonic), modern Yeni Mevlevihane Kapısı, was located between towers 50 and 51 and named after the suburb of Rhegion. It was also called Шаблон:Lang ("Gate of the Reds"), because it had been repaired in 447 by the dēmos of the Reds (Rousioi).
The gate (Шаблон:Polytonic), named so after a nearby church, was earlier known as the Fourth Military Gate. It lies between towers 59 and 60, and with a gatehouse of 26,5 m, it is the second-largest gate after the Golden Gate. Between the Gate of St. Romanus and the Gate of Charisius lay the so-called Mesoteichion ("Middle Wall"), a stretch of walls with a length of 1,250 metres. It was considered as the weakest part of the walls, because the ground descended towards the valley of the Lycus stream, as a result of which the walls lay lower than the opposing slopes. It was here that Mehmed II had placed most of his artillery, and much of this portion of the walls lies still in ruins today.
The gate known in Turkish as Topkapı, the "Cannon Gate", lies shortly after the Gate of St Romanus, between towers 65 and 66. Its name comes from the great cannon (the "Basilic") that was placed opposite it during the 1453 siege. This gate was earlier identified as the "civil" Gate of St Romanus.
The Fifth Military Gate (Шаблон:Polytonic) lies to the north of the Lycus stream, between towers 77 and 78. It is also identified with the Byzantine Gate of St Kyriake, and called Sulukulekapı or Hücum Kapısı, the "Assault Gate", in Turkish, because there the decisive breakthrough was achieved on the morning of May 29 1453.
The gate (Шаблон:Polytonic) is also known as Gate of Polyandrion or Myriandrion (Шаблон:Polytonic), because it led to a cemetery outside the Walls. A further corrupted form of the name, recorded during the siege of 626, is Koliandros. The last Byzantine emperor, Constantine XI, established his command here in 1453. In Turkish it isknown as Edirnekapı ("Adrianople Gate"), and it is here where Mehmed II made his triumphal entry into the conquered city. This gate stands on top of the sixth hill, and was the highest point of the old city at 77 meters.
The first postern was the so-called Gate of Christ from the Chi-Rō Christogram above it, lay between the two first towers of the main wall. It was known in late Ottoman times as the Tabak Kapı. Similar posterns are the Yedikule Kapısı and the gates between towers 30/31 and 42/43, just north of the "Sigma". On the Yedikule Kapısı, opinions vary as to its origin: some scholars consider it to date already to Byzantine times, while others consider it an Ottoman addition.
According to the historian Michael Doukas, on the morning of 29 May 1453, the small postern called Kerkoporta was left open by accident, allowing the first thirty or so Ottoman troops to enter the city. The Ottomans raised their banner atop the tower, signifying the beginning of the rout of the defenders, and the fall of the city. Scholars like van Millingen, Steven Runciman, and others , have traditionally placed the Kerkoporta at the end of the Theodosian Walls, between tower 96 and the so-called Palace of the Porphyrogenitus, or at the Komnenian Wall of Blachernae (see below). However, there is no evidence of a gate in the area, and it may be that the story is derived from the earlier legend concerning the Xylokerkos Gate, which several earlier scholars also equated with the Kerkoporta.
The impression made by the mighty Theodosian Walls on the Western Crusaders who encountered them can be seen in the 13th century Caernarfon Castle in Wales, built by Edward I of England as a royal residence, which is said to have been modeled on them. With the advent of siege cannons, however, the fortifications became obsolete, but their massive size still provided effective defence, as demonstrated during the Second Ottoman Siege in 1422. In the final siege, which led to the fall of the city to the Ottomans in 1453, the defenders, severely outnumbered, still managed to repeatedly counter Turkish attempts at undermining the walls, repulse several frontal attacks, and restore the damage from the siege cannons for almost two months. Finally, on 29 May, the decisive attack was launched, and when the Genoese general Giovanni Giustiniani was wounded and withdrew, causing a panic among the defenders, the walls were taken. After the capture of the city, Mehmed had the walls repaired in short order among other massive public works projects, and they were kept in repair during the first centuries of Ottoman rule.
A fortress (Ελληνικά. καστέλλιον) was in existence behind the Golden Gate by the early 1350s, when it was garrisoned by Catalan soldiers loyal to John VI Kantakouzenos. After Kantakouzenos' resignation in 1354, it was partially demolished by John V Palaiologos. In 1389-90 however, John V rebuilt and expanded the fortress, extending its walls all the way to the sea walls. Soon, John V was forced to flee there from a coup led by his grandson, John VII. John V was held out successfully in a siege that lasted several months, and in which cannons were possibly employed. In 1391 however, John V was compelled to raze the fort by Sultan Bayezid I, who otherwise threatened to blind his son Manuel, whom he held captive. Emperor John VIII Palaiologos attempted to rebuild it in 1434, but was thwarted by Sultan Murad II.
After the final capture of Constantinople, Sultan Mehmed II rebuilt the fort in 1457, again with seven towers (to the four pre-existing ones on the Inner Theodosian Wall - towers eight to eleven - three larger ones were added behind the wall), as the Yedikule Hisar (Turkish for "Fortress of Seven Towers"). During much of the Ottoman era, it was used as a treasury and state prison. The ambassadors of states currently at war with the Porte were usually imprisoned there. Amongst its most notable prisoners was the young Sultan Osman II, who was imprisoned and executed there by the Janissaries in 1622.
During the Napoleonic Wars, the fortress was the prison of many French prisoners, including the writer and diplomat Francois Pouqueville who was detained there for more than two years (1799 to 1801) and who wrote an extensive description of the area.
in the background, as they appear today in suburban Istanbul.]] In the northwestern corner of the city, the suburb of Blachernae with its important church of Panagia Vlacherniotissa was left out of the Theodosian walls. To defend it, in the face of the great Avar siege, a single wall was built, around 627, in the reign of Heraclius. In 814, Leo V the Armenian built a new wall in front of the Heraclean one to safeguard against Bulgarian raids. In the 12th century, when Blachernae had become the favored imperial residence, Manuel I Komnenos built a wall, starting from the end of the Theodosian Walls, to protect the imperial palaces, which was connected by a later wall (possibly under Isaac II Angelos) to the Heraclean wall. Despite all this, the defenses of the Blachernae section remained weaker than at the Theodosian Walls, and it was here the Crusaders of the Fourth Crusade managed to penetrate and first enter the city.
The Walls of Blachernae consist of four single walls built in different periods. Generally they are about 12-15 meters in height; thicker than the Theodosian Walls and with more closely spaced towers. Situated on a steep slope, they lacked a moat, except on their lower end towards the Golden Horn, where Emperor John VI Kantakouzenos had dug one. The fortification begins at the end of the Theodosian Walls with the Komnenian Wall, connected by the Angelian wall to the Heraclean wall, which in turn is connected to the Sea Walls at the Golden Horn. The wall of Leo V lies in front of the Heraclean wall.
The wall of Manuel Komnenos is an architecturally-excellent fortification, extending for 220 m, with 9 towers, the small gate (paraportion) of St. Kallinikos between the second and third towers, and one gate after the sixth tower, the modern Eğri Kapı (the "Crooked Gate"), which is identified with the old Kaligaria Pylē, the "Gate of the Bootmakers' Quarter". The Eğri Kapı is so named because the road in front of it detours sharply around a tomb, which is supposed to belong to Hazret Hafiz, a companion of the Prophet Muhammad, who died there during the first Arab siege of the city.
The Komnenian wall ends at the third tower from the gate, and the newer wall (from the late 12th century), architecturally much inferior, continues for about 400 metres. This wall has four square towers and a gate, the Gyrolimne Gate (Шаблон:Lang, from Argyrē Limnē, the "Silver Lake") between the second and third of them, now walled up, which led to the Blachernae Palace. The last stretch of the wall is adjoined by two structures: the Tower of Isaakios Angelos, built around 1188 as a residence for the Emperor, and the nearby building and tower known as Prisons of Anemas, dated to the 7th century but named after Michael Anemas, a general of Alexios I who was imprisoned there after a failed plot against the Emperor.
The wall of Heraclius begins from there and extends for about 100 metres to the Sea Walls. It has three strong hexagonal towers, and the Gate of Blachernae (Шаблон:Polytonic). The wall of Leo V complements it from the outside, forming a sort of rectangular fort, with an internal space of about 25 metres between the two walls. At the edge of the Leontian wall stands the Tower of St. Nicholas, originally built by Leo V and rebuilt by Emperor Romanus I Lecapenus. The Leontian Wall is thinner and of inferior construction to the Heraclean, and features four small towers along with a now collapsed gate, which formed the outer counterpart of the Blachernae Gate. Since the Sea Walls at the Golden Horn were built at a distance from the shore, a wall extended from the end of the Land Walls to the shoreline, the so-called Vrakhiolion, erected at the same time as the main Heraclean wall, in 627. It had a single gate, the "Wooden Gate" (Шаблон:Lang or Шаблон:Lang).
The land walls run through the heart of modern Istanbul, with a belt of parkland flanking their course. They are pierced at intervals by modern roads leading westwards out of the city. Many sections were restored during the 1980s, with financial support from UNESCO, but the restoration program has been criticized for destroying historical evidence, focusing on superficial restoration, the use of inappropriate materials and poor quality of work. This became apparent in the 1999 earthquakes, when the restored sections collapsed while the original structure underneath remained intact. The threat posed by urban pollution, and the lack of a comprehensive restoration effort, prompted the World Monuments Fund to include them on its 2008 Watch List of the 100 Most Endangered Sites in the world.
The sea walls enclosed the city on the sides of the Propontis (Sea of Marmara) and the gulf of the Golden Horn (Шаблон:Polytonic). Although the original city of Byzantium certainly had sea walls, traces of which survive, the exact date for the construction of the medieval walls is a matter of debate. For long, the seaward walls were attributed to Constantine I, along with the construction of the main land wall. However, the first actual reference to their construction comes in 439, when the urban prefect Cyrus of Panopolis was ordered to repair the city walls and complete them on the seaward side. This activity is certainly not unconnected to the fact that in the same year, Carthage fell to the Vandals, an event which signaled the emergence of a naval threat in the Mediterranean. Nevertheless, the walls are not specifically mentioned as extant until much later, around the year 700.
The Sea Walls were architecturally similar to the Theodosian Walls, but of simpler construction. They were formed by a single wall, considerably lower than the land walls, with inner circuits in the locations of the harbours. Enemy access to the walls facing the Golden Horn was prevented by the presence of a heavy chain or boom, installed by Emperor Leo III, supported by floating barrels and stretching across the mouth of the inlet. One end of this chain was fastened to the Tower of Eugenius, in the modern suburb of Sirkeci, and the other in Galata, to a large, square tower, the basement of which was later turned into the Yeraltı (underground) Mosque.
During the early centuries of its existence, Constantinople faced few naval threats. Especially after the wars of Justinian, the Mediterranean had again become a "Roman lake". It was during the first siege of the city by the Avars and the Sassanid Persians that for the first time, a naval engagement was fought off the city itself. However, after the Arab conquests of Syria and Egypt, followed later by Crete, an new naval threat emerged, prompting successive emperors to attend to the sea walls. They were renovated in the early 8th century under Tiberios III or Anastasios II, while Michael II initiated a wide-scale reconstruction, eventually completed by his successor Theophilos, which increased their height. During the siege of the city by the Fourth Crusade, the sea walls nonetheless proved to be a weak point in the city's defences, as the Venetians managed to storm them.
Following this experience, Michael VIII Palaiologos took particular care to heighten and strengthen the seaward walls after the recapture of the city in 1261, as he faced the further threat of a possible invasion by Charles d'Anjou.
The wall of the Propontis was built almost at the shoreline, with the exception of harbours and quays, and had a height of 12–15 metres, with 10 gates, 3 small gates, 188 towers and a total length of almost 8,460 metres, with further 1,080 metres comprising the inner wall of the Vlanga harbour. Several sections of the wall were damaged during the construction of the Kennedy Caddesi coastal road in 1956–57. From the Marble Tower to the cape at the edge of the ancient acropolis of the city (modern Sarayburnu, Seraglio Point), the wall's gates were:
The wall facing towards the Golden Horn, where in later times most seaborne traffic was conducted, stretched for a total length of 5,600 metres from the cape of St. Demetrius to the Blachernae, where it adjoined the Land Walls. Although much of the wall was demolished in the 1870s, during the construction of the railway line, its course and the position of most gates and towers is known with accuracy. It was built further inland, up to 40 metres from the shore, and was about 10 metres tall, with 17 gates (plus two added in Ottoman times) and 110 towers. The gates were, in order:
During the whole existence of the Byzantine Empire, the garrison of the city was quite small: the imperial guards and the small city watch (the kerketon) under the urban prefect were the only permanent armed force available. Any threat to the city would have to be dealt with by the field armies in the provinces, before it could approach the city itself. In times of need, such as the earthquake of 447 or the raids by the Avars in the early 7th century, the general population would be conscripted and armed, or additional troops would be brought in from the provincial armies.
In the early centuries, the imperial guard consisted of the units of the Excubitores and Scholae Palatinae. In time, they declined to parade-ground troops, but in the 8th century the Emperors, faced with successive revolts by the thematic armies and pursuing deeply unpopular Iconoclastic policies, established the imperial tagmata for their own security. Although the tagmata formed the core of imperial expeditionary armies and were often absent from the city, two of them, the Noumeroi and the Teicheiōtai remained permanently stationed in Constantinople, garrisoned around the Palace district or in various locations, such as disused churches, in the capital. These units were never very numerous, numbering a few thousands at best, but they were complemented by several detachments stationed around the capital, in Thrace and Bithynia.
The small size of the city's garrison was due to the uneasiness of Emperors and populace alike towards a permanent large military force, both for fear of a military uprising and because of the considerable financial burden its maintenance would entail. Furthermore, a large force was largely unnecessary, because of the inherent security provided by the city walls themselves. As historian John Haldon notes: "Providing the gates were secured and the defences provided with a skeleton force, the City was safe against even very large forces in the pre-gunpowder period."
, at the northern shore of the Golden Horn, are prominently featured. The water trench in front of the Theodosian walls at the western end of the city is also depicted, as well as the Maiden's Tower in the middle of the Bosporus.]]
Several fortifications were built at various periods in the vicinity of Constantinople, and can be said to have formed an integrated defensive system along with the city's main walls. The first and greatest of these is the 56 km long Anastasian Wall (Greek Anastaseio Teichos or Makron Teichos, "Long Wall"), built in the mid-5th century as an outer defense to Constantinople, some 65 km westwards of the city. It was 3.30 m thick and over 5 m high, but its effectiveness was limited, and it was abandoned at some time in the 7th century for want of resources to maintain and men to man it. For centuries thereafter, its materials were used in local buildings, but several parts are still extant.
In addition, between the Anastasian Wall and the city itself, there were several small towns and fortresses like Selymbria, Rhegion or the great suburb of Hebdomon ("Seventh", modern Bakırköy, so named from its distance of seven Roman miles from the city walls), the site of major military encampments. Beyond the Long Walls, the towns of Bizye and Arcadiopolis covered the northern approaches. These localities were strategically situated along the main routes to the city, and formed the outer defences of Constantinople throughout its history, serving to muster forces, confront enemy invasions or at least buy time for the capital's defences to be brought in order. It is notable that during the final Ottoman siege, several of them, such as Selymbria, surrendered only after the fall of Constantinople itself. In Asia Minor, their role was mirrored by the cities of Nicaea and Nicomedia, and the large field camp at Malagina.
Galata, then the suburb of Sykai, was fortified under Justinian, but the settlement declined and disappeared after the 7th century, leaving only the great tower (the kastellion tou Galatou) in modern Karaköy, that guarded the chain extending across the mouth of the Golden Horn. After the sack of the city in 1204, Galata became a Venetian quarter, and later a Genoese extraterritorial colony, effectively outside Byzantine control. Despite Byzantine opposition, the Genoese managed to surround their quarter with a moat, and by joining their castle-like houses with walls they created the first wall around the colony. The Galata Tower, then called Christea Turris ("Tower of Christ"), and another stretch of walls to its north were built in 1349. Further expansions followed in 1387, 1397 and 1404, enclosing an area larger than that originally allocated to them, stretching from the modern district of Azapkapı north to Şişhane, from there to Tophane and thence to Karaköy. After the Ottoman conquest, the walls were maintained until the 1870s, when most were demolished to facilitate the expansion of the city. Today only the Galata Tower, visible from most of historical Constantinople, remains intact, along with several smaller fragments.
The twin forts of Anadoluhisarı and Rumelihisarı lie to the north of Constantinople, at the narrowest point of the Bosporus. They were built by the Ottomans to control this strategically vital waterway in preparation for their final assault on Constantinople. Anadoluhisarı (Turkish for "Fortress of Anatolia"), also called Akçehisar and Güzelcehisar in earlier times, was constructed by Sultan Bayezid I in 1394, and initially consisted of just a 25 m high, roughly pentagonal watchtower surrounded by a wall. The much larger and elaborate Rumelihisarı ("Fortress of Rumeli") was built by Sultan Mehmed II in just over 4 months in 1452. It consists of three large and one small towers, connected by a wall reinforced with 13 small watchtowers. With cannons mounted on its main towers, the fort gave the Ottomans complete control of the passage of ships through Bosporus, a role evoked clearly in its original name, Boğazkesen ("cutter of the strait/throat"). After the conquest of Constantinople, it served as a customs checkpoint and a prison, notably for the embassies of states that were at war with the Empire. After suffering extensive damage in the 1509 earthquake, it was repaired, and was used continuously until the late 19th century.