Defensive walls 5630 m long were erected at the beginning of the 5th century. under Emperor Theodosius II to protect Constantinople from the barbarians, when the city grew and went beyond the walls that were provided for by its founder, Constantine the Great. Earthquakes and barbarian sieges forced the walls to be regularly rebuilt and strengthened, as a result of which they turned into a whole complex of fortifications. Later they were fortified with hexagonal and octagonal towers 20 meters high - there were up to 100 of them. Ten main gates were also built in the Wall (five public and five military).
Mehmed the Conqueror, after the capture of Constantinople, added three new ones to the four towers of Theodosian walls, connected everything with walls and got a small fortress, known as “Seven Towers” - it was used as a prison, archive and treasury.
As Istanbul grew in the late 19th and early 20th centuries, the Theodosian walls began to be demolished, but still some sections of the wall have been preserved in different parts of Istanbul and are available for inspection.