1.Historical context

The original fortifications of Constantinople were built by its founder, Emperor Constantine I (307-337). According to the tradition, he drew the line along which the land walls of city would be built. However, from the end of the 4th c., the increase of population in Constantinople resulted in a lack of space and the tendency to extend the urban web outside the walls of Constantinople. At the same time, the appearance of the Huns in the northern border of Byzantine Empire in the beginning of the 5th c. rendered essential the construction of a more powerful defensive line, since the western part of the fortifications of Constantinople was easiest to take with an attack from the plain of Thrace.¹

For these reasons, in the beginnings of the reign of Theodosios II (408-450), Anthemios, praetorian prefect the East and governor of the empire (because the emperor was still underage and did not take part in the decision-making) undertook the initiative to erect a new line of defensive walls around two kilometres westwards of the walls of Constantine. The new walls were named Theodosian, in honour of the emperor. With their later additions and rebuilding, they protected effectively the capital of the Empire for roughly one millennium and they are considered by modern researchers as an exceptional example of military architecture of Late Antiquity and Middle Ages.

2. The construction of the Theodosian walls

Scholars have not concluded on the exact date of the construction of the walls, but in all likelihood the decision for the erection of new fortifications was taken shortly after 408 and the initial works had been completed by 413.² The inhabitants of Constantinople worked for their building, while the expenses were covered by contributions by the wealthy citizens and the Demoi. One third of the income from taxation was used to cover the cost of their maintenance.

The first to be built was the main wall (in the contemporary sources it is mentionned as “inner” or “great wall”). It was 5.650 metres long, it had 96 towers and it extended from the coast of Propontis until the region of Blachernai, which was protected by a pre-existing wall. In 447 the wall suffered serious damages beacause of a powerful earthquake, which destroyed 57 towers. At the time, the situation was critical, because the Huns under the leadership of Attila threatened Constantinople. Thus, with the initiative of prefect Constantine, the citizens hurried to repair the wall, a work that was completed in two months.³ At the same time, an outer wall was also built, also referred to as “proteixisma”, which also reached until Blachernai, and a moat was also opened which extended from Propontis until the Golden Horn. A little earlier, in 439, the prefect Cyrus Panopolites had extended the sea walls so that they would be connected with the new defensive line.⁴ In the ends of the two walls there were the brachialia, small walls that extended to the sea and restrained access to the land in front of the sea wall.

3. Description of the Theodosian walls

3.1. The main wall

The inner wall was founded on natural rock; it was 5 metres thick, 10 metres high and had bastions of 2 metres. Its two faces were built by carefully squared limestone, while the core was rubble set in mortar. At intervals bands of five courses of red bricks went right through the wall, binding it together and creating a fine aesthetic effect.⁵

Every 60-70 metres along the wall there was a tower; most of these towers were square, 20 were polygonal, mainly octagonal. In the south part of the walls square and octagonal towers interchanged, while in the middle part almost all the towers were square. The reasons of this alternation are not known, but apparently it was not dictated by any strategic purpose. The towers were 15-16 metres high and they projected 10 metres from the wall. Their masonry (massive walls, 2 m. thick), which is not connected with the wall, shows that they were erected after the the enceinte was completed. The towers had two levels, which for reasons of safety did not communicate with each other. The ground floor was still useful as warehouse or it was ceded to the use of citizens, while the upper storey was accessible only from the wallwalk, and ballistic machines (catapults) were placed there. The roofs of the towers were crowned by battlements.

3.2. The outer wall

At 13, 50 metres from the inner wall (the distance was decreased to less than 4 metres around the towers) the outer wall or proteixisma was situated. In all probability it was built after the earthquake of 447, in order to ensure the defence of city in case a new earthquake damaged the great wall (the low height of the outer wall made it more resistant to earthquake shocks). In this period (5th c.) the existence of an outer wall was usual in the fortifications of other cities too (such as in Thessalonica and Nicaea). The outer wall was 4 metres high above the level of the peribolos (the wide terrace between the two walls), but, since the area on the outside was at a lower level, the height of its external side was double. It was 4,50 m. thick; 1,30 were compact wall and the rest consisted of 2.500 relieving arches; on the lunette of each one of them a loophole was opened. The arches supported the wallwalk that were crowned with battlements.

The towers of the outer wall were alternately square and semicylindrical, placed in such a way, so that behind them stood the curtain of the main wall, and the towers of the main wall stood mainly behind the curtain of the outer wall. This was obviously intended from the start, so that the two walls covered each other. The towers were hardly 0,50 metres higher than the outer wall and projected around 5 metres from it. On the upper-storey walls loopholes were opened on the level of the wallwalk, and their tops were crenellated. Certain square towers had also a chamber with a small door leading outside on ground level, in order to facilitate the sorties of the defenders.⁶

3.3. The moat

Around 20 metres from the outer wall (the outer walk was called parateichion) there was the moat, the first line defence of the Theodosian walls. It was 15-20 metres wide and 5-7 metres deep.⁷ Its sides were built with stones, while per intervals there were stone dams which prevented the water from pouring into the Golden Horn because of the altitude difference. Above the inner side of the moat raised low wall, 2 metres high.⁸

4. The gates

There were many gates in the Theodosian walls, the most important of which were, beginning from Propontis, the First Military Gate (known and as Gate of Christ), the Golden Gate (a pre-existing triumphal arch that was incorporated to the Theodosian wall ), the Second Military Gate, the Gate of Pege or of Selymbria (from this point the soldiers of Alexios Strategopoulos entered in the City in July 1261), the Third Military Gate, the Gate of Reghion, the Fourth Military Gate, the Gate of Saint Romanos or Resion, the Fifth Military Gate and finally the Gate of Charision or Andrianople. In the inner surrounding wall the gates were framed by strong square towers, apart from the gate of Charision, where the towers were semi-circular.⁹

5. Later additions

The triple area of defence (moat, outer wall, inner wall), terminated 1000 metres away from the Golden Horn, rendering the region of the Blachernai the most susceptible point of defence of Constantinople, targeted by the Avars in 626 and the knights of the fourth Crusade in 1203-1204. As it is natural, the later efforts of Byzantines to strengthen the land walls of Constantinople were focused in the construction of the new walls in this particular region.

The first addition after the 5^th c. in the Theodosian walls was made by Herakleios (610-641) after 626. Because he wanted to protect the -until then defenceless- church of Virgin Mary of Blachernai (in the miraculous intervention of which the citizens attributed the repulse of the Avars), the emperor built or strengthened a pre-existing wall, the so-called Pteron, from the Blachernai until the Golden Horn. The new wall was reinforced with small square towers. In 813 emperor Leo V the Armenian (813-820), strengthened the fortification of the region which was waiting for the attack from the Bulgarians of Kroumos, by building a high outer wall 20 metres away from the Pteron. The great height of the wall of Leo V complicated the overlying shot from the Pteron, and had as a result to make the last one useless. Later however, during the reign of Michael II (820-829), the Pteron was reinforced with three hexagonal towers of 26 metres. Catapults were placed in the top floor of these towers which could shoot over the wall of Leo.

The last Byzantine addition in the Theodosian wall was made by the emperor Manuel I Komnenos (1143-1180), who built one long wall in order to fortify the region of the palace of Blachernai from the West. The new wall (the different construction of which is immediately distinguished in relation to the Theodosian wall) was 15-18 metres high and 3, 75 metres thick, strengthened in its interior with buttresses. It had massive petal-shaped, circular, square and polygonal towers.

6. Repairs

Apart from the additions, various repairs in the Theodosian walls and towers are occasionally mentioned (mainly in inscriptions), either after the damage by earthquakes or hostile action, or in the context of preparations for the repulse of an attack. The main phases of repairs are dated in the last years of Justinian I (527-565) and his successors, in the beginning of the 8^th c. (Justinian II, Anastasius II and Theodosius IV, obviously while waiting an attack by the Arabs), around 740 after an earthquake, after the recapture of the Constantinople by Michael VIII Palaiologos (1258-1282) and his successors, as well as in the middle of the 14^th c., in the midst of the civil war between John V Palaiologos and John VI Kantakouzenos. The last line of repairs is dated between 1432 and 1441 and it was focused in the exterior wall, which constituted also the in the main defence of the Byzantines at the siege of 1453.

7. The land walls after 1453

7.1. Ottoman additions and repairs

The usefulness of the Theodosian wall did not cease with the fall. On the contrary, one of the first concerns of sultan Mehmet II (1451-1481) was the repairs of parts of the wall that had suffered the bigger damage during of siege. In 1457 the Ottomans proceeded in the last addition in the history of walls, manufacturing the fortress of Yedikule in southern end of the walls. The fortress was petal-shaped and it was created with the construction of three towers in the interior of the main wall, which were linked with each other with a strong wall. Its fifth side was the incorporated into the fortress part of the Theodosian walls between towers 8 and 11; this part also included the Golden Gate with its two towers. The four Byzantine towers and the three newer ones are those that gave to the fortress its name (Yedikule/ Heptapyrgion, mean. a fortress of seven towers). Repairs in the Theodosian wall took place also in 1509, as well as in 1635. Then the walls were reconstructed to a large degree, and at the same time the surfaces were covered with mortar. A characteristic of the repairs in the Ottoman period are the scattered “patches” in the areas made of plinth along the Theodosian wall, where new plinths were placed in parallel with the facade of the wall and not vertically. In 1656 new repairs took place, while the walls suffered important damages during the big earthquakes of 1690 and 1709. The last effort to reconstruct the land walls was an initiative of sultan Achmet III and is dated between 1722 and 1724.¹⁰

7.2. The restoration program in the 20th c.