The triangular promontory on which old Istanbul is located is surrounded by city walls. The 22 km long walls date back to the 5th century, the Roman era. The original city of Byzantium expanded toward the west and new city walls were erected four times, each time enlarging the city further.

The peninsula was easily defensible. The terrain to the west is quite flat in the direction of the Balkans, but the gigantic walls ensured protection on the landside.

The shores of the Golden Horn and the Marmara were also defended by a single, but sturdy wall.

Nothing has survived from the walls built around the acropolis of Byzantium, the second wall built by Septimius Severus in the 3rd century or the third wall built in 320 by Constantine the Great.

The land walls start from the seashore and, after crossing hills and valleys, join the sea wall on the banks of the Golden Horn.
Inscriptions from different eras indicate the restorations in the walls. The land walls are 6,492 m long. Behind the moat and the first row of walls and battlements rise the higher main wall with 96 towers.

Most of the original gates have survived to our day. As a result 'of the restoration and renovation work that began in the 1980's and is still continuing, the vicinity of the walls has been improved and the some areas turned into public parks.