Walls of Constantinople

Map showing Constantinople and its walls during the Byzantine era

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 are one of the greatest and most complex fortification 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). Only the advent of gunpowder siege cannons rendered the fortifications obsolete, resulting in the final siege and fall of Constantinople to the Ottomans on 29 May 1453.

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 in the past twenty years, which allows the visitor to appreciate their original appearance.

The Land Walls

The Walls of Byzantium and Constantine

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.^[1] However, soon after he rebuilt it, appreciating the city's strategic importance, and endowed it with many monuments and a new set of walls, increasing its area.

When Constantine the Great moved the capital of the Empire to Byzantium, which he refounded as Nova Roma, 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.^[2][3] 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 Constantine 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; however, only the Old Golden Gate still survived to late Byzantine times, until destroyed by an earthquake in 1509. Already by the early 5th century however, Constantinople had expanded outside the Constantinian Wall, in the extra-mural area known as the Exokionion.^[4]

The Theodosian Walls

Restored section of the Theodosian Walls at the Selymbria Gate. The Outer Wall and the wall of the moat are visible, with a tower of the Inner Wall in the background

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.^[5] The new wall, which became known as the Theodosian Wall (Greek Theodosianon Teichos), was built under the direction of Anthemius, the Praetorian prefect of the East, and completed in 413.^[6] 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 Floros (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.^[5] At the same time, a second outer wall was added, and a wide ditch opened in front of the walls.^[7]

The Second Military Gate or Gate of Belgrade

The walls were built of alternating layers of stone and brick in two lines of defense which adjoined the ditch. The Inner Wall (Esō Teichos or Mega Teichos, "Great Wall") was a solid structure, 5 metres thick and 12 metres high. It was strengthened with 96 towers, mainly square but also octagonal or hexagonal, 18-20 metres tall, every 55 metres.^[8] 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.^[9] The Outer Wall (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 metres.^[10] 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 in the middle distance between the Inner Wall's towers.^[11] 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.^[12] 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, which could be flooded, 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.^[13]

Detailed course and description of the Land Walls (from south to north)

The walls stretched for about 5.5 km from south to north, from the Marble Tower, Turkish Mermer Kule (or "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. The wall contained 10 main gates, plus an unknown number of small posterns, which were usually walled up in the event of a siege. The five public gates led across the moat on bridges, while the five so-called "Military Gates", known initially only by their numbers, led to the outer sections of the walls. In order, from south to north, these gates were:

1. the First Military Gate (Pylē tou Prōtou), or Gate of Christ, named so because of the Chi-Rō Christogram inscribed on it, today known as the Tabak Kapı.
2. the Golden Gate (Greek Chrysē Pylē, Latin Porta Aurea, Turkish Altınkapı or Yaldızlıkapı), which was a triumphal arch from the reign of Theodosius I, originally standing alone, outside the Constantinian Wall, over the Via Egnatia. It was incorporated in the Theodosian Walls, serving as the state entrance into the capital, especially for the occasions of a triumphal return of victorious emperors from battle.^[14] It was architecturally elaborate, built of large square blocks of polished marble fitted together without cement, with three arches. During later years, two great flanking towers of the same material were added. Upon the gates were placed sculpted bronze elephants, flanked by winged Victories. Behind the gate lies the Ottoman-era Yedikule Fortress (see below). Since the main Gates were usually kept closed, a smaller gate exists after the Fort, the Small Golden Gate (Mikra Chrysē Pylē), modern Yedikule Kapısı, which was used for everyday traffic.
3. the Second Military Gate (Pylē tou Devterou), the greatest of the military gates. 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.
4. the Gate of Melantias (Porta Melantiados) or Selymbria Gate (Turkish Silivri Kapısı), also known as Zōodochos Pēgē after a monastery outside the Walls, where the forces of the Empire of Nicaea under General Alexios Strategopoulos entered and retook the city from the Latins on 25 July 1261.^[15]
5. the Third Military Gate (Pylē tou Tritou) at the section known as the "Sigma", today walled up.
6. the Gate of Rhegium (Pylē Rēgiou), modern Yeni Mevlevihane Kapısı, also named Pylē Rousiou ("Gate of the Reds"), because it had been repaired in 447 by the dēmos of the Reds.
7. the Fourth Military Gate (Pylē tou Tetartou), south of modern Millet Jaddesi.
8. the Gate of St. Romanus (Porta Agiou Rōmanou), named so after a nearby church, is called Topkapı, the "Cannon Gate" today, because of the great cannon (the "Basilic") that was placed opposite it during the last siege of Constantinople. Emperor Constantine XI established his command here, at the central and most threatened stretch of the walls.
9. the Fifth Military Gate (Pylē tou Pemptou), called Hüjum Kapısı, the "Assault Gate", in Turkish, because there the decisive breakthrough was achieved on the morning of May 29, 1453.
10. the Gate of Charisius (Porta Charisiou) or Polyandrion (Porta Polyandriou, named so because it led to a cemetery outside the Walls), in Turkish Edirnekapı ("Gate of Adrianople"), 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 city at 77 metres.

At the very end of the Theodosian Walls is the postern called the Xylokerkos Porta or Kerkoporta, after a wooden circus (amphitheatre) that existed there. This gate was left open on the fateful 29 May, apparently accidentally but possibly through treachery, and through it the Janissaries first entered the city. A large plaque today marks the spot.

The restored Gate of Charisius or Adrianople Gate, where Sultan Mehmed II entered the city.

The stretch of walls between the Gate of St. Romanus and the Gate of Charisius, with a length of 1,250 metres, was known as the Mesoteichion ("Middle Wall"). It was considered as the weakest part of the walls, because the ground descended towards the valley of the Lycus River, and as a result the walls lay lower than the opposing slopes. It was here that Mehmed II had placed most of his artillery, and as a result, much of this portion of the walls lies still in ruins today.

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 modelled 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.

Many sections were restored during the 1980s, with financial support from UNESCO, but the restoration programme has been criticised for focusing on superficial restoration and poor quality of work, which became apparent in recent earthquakes, as well as destroying historical evidence. ^[16] Nonetheless, the restored sections give a fairly accurate image of the walls as they stood during Byzantine times. The wall runs through the suburbs of modern Istanbul, with a belt of parkland flanking their course. The walls are pierced at intervals by modern roads leading westwards out of the city.

The Yedikule Fortress

The Castle of Seven Towers (1827)

The first fortress behind the Golden Gate began being built during the reign of John I Tzimiskes and was completed under Manuel I Komnenos. That fort (Kastellion) had five towers, and was hence also named Pentapyrgion. It was destroyed after the first fall of the city to the Fourth Crusade, and rebuilt only in 1350 by John VI Kantakouzenos. The new fort featured five octagonal towers, and together with the two marble towers of the Golden Gate, seven in total, becoming known as the Eptapyrgion ("Seven Towers"). In 1391 however, John V Palaiologos was forced 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 (four on the Inner Theodosian Wall - towers eight to eleven - and three larger ones behind), 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. Amongst its most notable prisoners was the young Sultan Osman II, who was imprisoned and executed there by the Janissaries in 1622.^[17]

The Walls of Blachernae

The section of the Theodosian Walls that adjoins the walls of Blachernae, with the Palace of Porphyrogenitus 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 favoured 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.^[18] Despite all this, the defences of the Blachernae section remained weaker than at the Theodosian Walls, and it was here the Crusaders of the Fourth Crusade managed to penetrate them and first enter the city.

The Walls of Blachernae consist of four single walls built in different periods. Generally they are about 12-15 metres in height; thicker than the Theodosian Walls and with more closely spaced towers, while lacking a moat. 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.^[19]

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 ca. 400 metres. This wall has four square towers and a gate, the Gyrolimne Gate (from Argyrē Limnē, the "Silver Lake") between the second and third of them, now walled up, which led to the Blachernae Palace.^[20] 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.^[21]

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 (Pylē Vlachernōn). The wall of Leo V complements it from the outside, forming a sort of rectangular fort, with an internal space of ca. 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" (Xyloporta).

The Sea Walls

The first seaward walls were ordered built by Constantine I along with the main land wall, and enclosed the city on the sides of the Propontis (Sea of Marmara) and the gulf of the Golden Horn (Chrysoun Keras), but scant information survives regarding them. It is very likely, however, that the later walls followed their course. In 439, after the initial enlargement of the city, Theodosius II ordered the then-Praetorian prefect of the East, Cyrus Panopolites, to extend the old sea walls to encompass the entire city.^[22] The construction of the walls was similar to, but simpler than, the Theodosian Walls. It consisted of a single wall, relatively low, as no threat was then expected from the sea, where the Roman navy enjoyed undisputed supremacy. Furthermore, according to Helmuth von Moltke, "the Bosphorus currents and south-west wind (Lodos) made it almost impossible for warships powered by oarsmen or sails to attack."^[5] Enemy access to the walls facing the Golden Horn was prevented by the presence of a heavy chain, 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.^[5]

However, after the Arab conquests of Syria and Egypt, followed later by Crete, the naval threat intensified, prompting successive emperors to attend to them. Anastasios II first renovated them in the early 8th century, while Michael II initiated a wide-scale reconstruction, eventually carried out by his successor Theophilos, which increased their height.^[23] 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.^[24]

Following this bitter 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 Propontis Wall

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 8460 metres, with further 1080 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.^[5] From the Marble Tower to the cape of St. Demetrius at the edge of the ancient acropolis of the city (modern Sarayburnu, Seraglio Point), the wall's gates were:

1. the Gate of St. John Studites (Pylē Agiou Iōannou tou Stouditou), modern Narlıkapı ("Gate of Roses"), which led to the important monastery of the same name.
2. the Gate of Psamathos (Porta Psamatheos, Turkish Samatya Kapısı), leading to the suburb of Psamathia.
3. the Gate of St. Aemilianus (Pylē Agiou Aimilianou, Turkish Davutpaşa Kapısı), before the harbours of Eleutherios and Theodosios.
4. the Vlanga Gate (Porta Vlaggas), at the mouth of the River Lycus, within the harbours. It was demolished after the Ottoman conquest, and a new gate (Yenikapı) build in its place.
5. the Kontoscalion Gate (Porta Kontoskaliou, Turkish Kumkapı), at the harbour of the same name.
6. the Iron Gate (Sidēra Pylē), leading to and from the harbour of Sophia or Sophianon (Limēn Sofianōn), also called harbour of Julian (Limēn Ioulianou). In Turkish it is called Kadırgalimanı Kapısı.
7. the Bull and Lion Gate (Porta Vōos kai Leontos, shortened to Voukoleōn), which led to the harbour and imperial palace of Bucoleon, in Turkish Çatladıkapı.
8. an unnamed gate, at the southeastern edge of the Imperial quarter, modern Ahırkapısı.
9. an unnamed gate, at the southeastern edge of the Imperial quarter, modern Balıkhane Kapısı (it lies immediately within the later perimeter of the Topkapı Palace).
10. the Gate of St. Lazarus (Porta Agiou Lazarou), at the ancient Temple of Poseidon.
11. the Postern of the Odegetria (Porta tēs Odēgētrias), at the Palace of Mangana, modern Demirkapı.
12. the Postern of Michael Protovestiarius (Porta Mikhaēl Prōtovestiariou), today Değirmen Kapı.
13. the Eastern Gate (Eōa Pylē) or Gate of St. Barbara (Pylē Agias Barbaras), in Turkish Top Kapısı, from which Topkapı Palace takes its name.

The Golden Horn Wall

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 ca. 10 metres tall, with 17 gates and 110 towers. The gates were, in order:^[5]

1. the Gate of Eugenios (Pylē Evgeniou), leading to the Prosphorion harbour. It was named after the nearby 4th century Tower of Eugenius, where the great chain that closed the entrance to the Golden Horn was kept and suspended from. The gate was also called Marmaroporta ("Marble Gate"), because it was covered in marble. In Turkish it is named Yalıköşkü Kapısı.
2. the Gate of Bonos (Porta Vōnou).
3. the Neorion Gate (Pylē Neōriou, "Shipyard Gate") or Horaia Gate (Ōraia Pylē, "Beautiful Gate").
4. the Ikanatissa Gate (Porta Ikanatissēs).
5. the Gate of St. Mark (Porta Agiou Markou) or Hebrew Gate (Evraikē Pylē), as it led to suburbs inhabited by Venetians and Jews, modern Balıkpazarı Kapısı.
6. the Gate of the Perama (Pylē Peramatos) from which the ferry to Pera (Galata) sailed.
7. the Gate of St. John of Cornibus, in Turkish Zindan Kapısı
8. the Gate of the Drungarii (Pylē Drouggariōn), modern Odunkapısı.
9. the Ayazma Kapısı Gate.
10. the Gate of the Plateia (Pylē Plateias), modern Unkapanı Kapısı..
11. the Gate of Eis Pegas (Pylē eis Pēgas), modern Cibali Kapısı.
12. the St. Theodosia Gate (Pylē Agias Theodosias), modern Ayakapı.
13. the Gate of Dexiokrates (Pylē Dexiokratous), modern Yenikapı.
14. the Petrion Gate (Pylē Petriou, Turkish Petri Kapısı), one of the two gates of the Petrion Fort, formed by a double stretch of walls. The gate of the fort's inner wall, which led to the city, was called the Gate of Diplophanarion.
15. the Phanar Gate (Pylē Fanariou, Turkish Fener Kapı), the second gate of the Petrion Fort, named after the local lighthouse. It was in this area that the Venetians under Enrico Dandolo successfully climbed the walls in 1204.
16. the Royal Gates (Vasilikai Pylai), in Turkish Balat Kapı ("Palace Gate"), which led to the Palace of Blachernae.
17. the Kynegos Gate (Pylē Kynēgou, "Gate of the Hunter").
18. the Gate of St. Anastasia (Pylē Agias Anastasias).
19. the Koiliomene Gate (Koiliōmenē Porta), in Turkish Ayvansaray Kapısı near the Church of St. Thecla.

Fortifications around Constantinople

The oldest surviving map of Constantinople, dated from 1422. The fortifications of Constantinople and of Galata, 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), 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.^[25]

The Walls of Galata

Galata, then the suburb of Sykai, was not fortified during most of the Byzantine period, save the great tower that guarded the chain extending across the mouth of the Golden Horn. However, 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.^[26] After the Ottoman conquest, the walls were maintained until the 1870s, when most were demolished to facilitate the expansion of the city.^[27] Today only the Galata Tower, visible from most of historical Constantinople, remains intact, along with several smaller fragments.^[5]

The Anadolu and Rumeli Fortresses

The Rumelihisarı Fortress, seen from the Bosporus.

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.^[27] 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"). 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.^[