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. 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 Eðri Kapý (the "Crooked Gate"), which is identified with the old Kaligaria Pylē, the "Gate of the Bootmakers' Quarter". The Eðri Kapý 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 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. 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 (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 walls of Constantinople are the greatest surviving example of European medieval military architecture in the world. They withstood numerous sieges until being finally overcome by the artillery of Mehmet the Conqueror in 1453, and exist today as a time capsule of Byzantine and Medieval history. This book examines the main defensive system protecting the landward side of the city, which consisted of three parallel walls about 5 miles long. The walls defended the city against intruders, including Attila the Hun, before finally being breached by European knights during the Fourth Crusade in 1204 and, ultimately, destroyed by Turkish artillery in 1453.
The suburb of Blachernae in the Northwest of the city was outside the walls. In around the 12th Century, it was decided to extend the Land Walls in a loop around Blachernae. This was a single wall, rather than the double system used along the rest of the Land Wall. The emperors then built a palace in the area, and it became their favoured residence in later centuries, although they still kept the Great Bucoleon Palace south of the Hippodrome.