THE CITY WALLS OF ISTANBUL

THEODOSIUS' STONE CURTAIN
From Antiquity to the Medieval Ages, it had been a military tradition to
protect a city by building walls around it. In this regard, the high city
walls of Istanbul were of great importance in the defense of the city,
which had been blockaded many times.
Walls surrounding istanbul constituted "the most prominent weapon" of the city, which is significant since the city had been the victim of blockades several times and had to defend itself against multiple armies that attempted to conquer it.
Unfortunately, most of the city's walls are not standing today. Of Istanbul's walls, which were built by the Byzantine Emperor Theodosius II, those standing today belong to three different sections, "Golden Horn Walls," "Marmara Walls" & " Land Walls."
The walls extending from the shores of the Golden Horn in Ayvansaray to the shores of the Marmara Sea in Yedikule are called the "City Land Walls." Istanbul's City Land Walls, which could be considered one of the most advanced defense plans of late Antiquity, had guarded the city for approximately a millennium.
The most significant feature of the City Land Walls is that they were built with three barriers or layers in contrast to other city walls.
Main walls are situated at the rear, then a trench, then the second, outer line of the walls.
These Land Walls, which are 6.5 km long, were damaged during the Ottoman blockade, but they were restored after the Ottoman conquest of the city, and they are the most durable of the remaining walls of the city. Marmara City Walls are located between Sarayburnu & Yedikule along the shoreline. These city walls were built to guard the city against military attacks from the sea. The Marmara City Walls, most of which have been damaged, were 8.5 km long at first. The height of the walls was between 12 and 15 meters on average, but the bastions are 20 meters in height. Some parts of these walls, which have 188 bastions and 36 gates in total, were damaged in the following centuries due to the construction of railways and overland routes.
Golden Horn City Walls lying between Ayvansaray and Sarayburnu, which cross the entire Golden Horn, are comprised of only one wall.
Old maps of Istanbul show how the city walls surrounded the old city. A noteworthy part of the walls still stands today. the walls were restored many times both by Byzantine and the Ottoman empires.