The place where Istanbul was first established, in other words, its center is the Historic Peninsula. It has been the city of the Roman, the Eastern Roman, the Ottoman Empire, and the Republic of Turkey. The walls, which are important for defense, have come to their final form in time with their size and borders. Land, Golden Horn, and Marmara walls combine to form a rough triangle and surround the Historical Peninsula of Istanbul. The walls consist of architectural elements such as towers, walls, gates, battlements, and stairs. Land, Golden Horn, and Marmara walls differ in terms of the importance given to them. They are double or single-row, contain additional security elements such as a moat, and are flat or shaped according to their location. The article gives information about the architectural features of the city walls in the Historical Peninsula of Istanbul. The similarities and differences with each other are emphasized. The characteristics of the city walls in the Sultanahmet Region, which is part of the Marmara sea walls that are strong and continuous today, are conveyed. The walls are discussed in terms of their form and the factors affecting them. The sea walls of the Sultanahmet Region are examined in palaces, constructions adjacent to the city wall, straight walls, dynamic walls, sheltered spaces, connection points, walls that have lost their authenticity with their close environment, and spaces inside the city walls. Visual materials such as maps, drawings, engravings, and photographs are used to give information.

Keywords: Istanbul Historical Peninsula, Sultanahmet Region, sea walls