Like Severus before him, Constantine began to punish the city for siding with his defeated rival, but soon he too realized the advantages of Byzantium‘s location. During 324–336 the city was thoroughly rebuilt and inaugurated on 11 May 330 under the name of “Second Rome“. The name that eventually prevailed in common usage however was Constantinople, the “City of Constantine” (Greek Κωνσταντινούπολις, Konstantinoupolis). The city of Constantine was protected by a new wall about 2.8 km (15 stadia) west of the Severan wall. 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 his son Constantius II (r. 337–361). Only the approximate course of the wall is known: it began at the Church of St. Anthony at the Golden Horn, near the modern Atatürk Bridge, ran southwest and then southwards, passed east of the great open cisterns of Mocius and of Aspar, and ended near the Church of the Theotokos of the Rhabdos on the Propontis coast, somewhere between the later sea gates of St. Aemilianus and Psamathos.
Already by the early 5th century however, Constantinople had expanded outside the Constantinian Wall, in the extramural area known as the Exokionion or Exakionion. The double Theodosian Walls located about 2 km to the west of the old Constantinian Wall, were erected during the reign of Emperor Theodosius II (r. 408–450), after whom they were named. The work was carried out in two phases, with the first phase erected during Theodosius’ minority under the direction of Anthemius, the praetorian prefect of the East, and was finished in 413 according to a law in the Codex Theodosianus. An inscription discovered in 1993 however records that the work lasted for nine years, indicating that construction had already begun circa 404/405, in the reign of Emperor Arcadius (r. 395–408). This initial construction consisted of a single curtain wall with towers, which now forms the inner circuit of the Theodosian Walls.
Both the Constantinian and the original Theodosian walls were severely damaged, however, in two earthquakes, on 25 September 437 and on 6 November 447. The latter was especially powerful, and destroyed large parts of the wall, including 57 towers. Subsequent earthquakes, including another major one in January 448, compounded the damage. Theodosius II ordered the praetorian prefect Constantine to supervise the repairs, made all the more urgent as the city was threatened by the presence of Attila the Hun in the Balkans. Employing the city’s “Circus factions” in the work, the walls were restored in a record 60 days, according to the Byzantine chroniclers and three inscriptions found in situ. It is at this date that the majority of scholars believe the second, outer wall to have been added, as well as a wide moat opened in front of the walls, but the validity of this interpretation is questionable; the outer wall was possibly an integral part of the original fortification concept.
Throughout their history, the walls were damaged by earthquakes and floods of the Lycus River. Repairs were undertaken on numerous occasions, as testified by the numerous inscriptions commemorating the emperors or their servants who undertook to restore them. The responsibility for these repairs rested on an official variously known as the Domestic of the Walls or the Count of the Walls, who employed the services of the city’s populace in this task. After the Latin conquest of 1204, the walls fell increasingly into disrepair, and the revived post-1261 Byzantine state lacked the resources to maintain them, except in times of direct threat.