The length of the historical walls surrounding Istanbul is twenty-two kilometers. There are ninety bastions on the land side walls. The ramparts surrounding Istanbul were built the first time in the 5th century, and were renewed four times due to demolition and re-building. During the era of Theodosius II (408-450) the ramparts of Istanbul stretched from Sarayburnu to Ayvansaray along the Golden Horn, to Yedikule along the Marmara, from Yedikule to Topkapı, and from Topkapı to Ayvansaray. The ramparts are a total of 22 km long; on the Golden Horn they are 5.5 km long. The ramparts are 7.5 km long on land and 9 km. long on the Marmara coastline. The land walls are composed of three sections, the moat, the external ramparts, and the internal ramparts. The moats are today used as agriculture fields. With a projection of 10 meters from the rampart walls, the towers have a square plan and are generally 25 meters high. They have windows, doors and vaults. The doors and stairs between the internal ramparts and the external ramparts are still visible. The internal ramparts and bastions are made of sandstone and bricks. The external walls, however, are mainly box walls or casemate walls. All these moats, bastions, and external and internal ramparts are 70 meters wide. They include corridors and small holes. On the Marmara and Golden Horn walls there are no moats or external ramparts. The width of these ramparts is 5 meters, and the height is 15m. The bastions are 20 meters high, On the Marmara side, there are 103 bastions, and 94 on the Golden Horn side. Yedikule, Sulukule, Anemas, İsaakios, Mermerkule, and Arapkule are historically important. Most of them were used as dungeons or prisons, and some also served as mints.

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