As you drive from the airport into the city you will definitely notice half demolished sections of the Byzantine city-walls. These walls were originally built in the 5th century with the others by Theodosios II. These walls have followed the historical development of the city. These land walls especially are lit during the night to give a thrilling atmosphere as you enter the city. It feels like you are entering ancient Constantinople in the present day.
The walls visible today are approximately 20 kilometres long. They are made up of three sections: the Land Walls, Marmara Walls and the Golden Horn Walls (shown in the photograph). You cannot visit these walls but you can get very close to experience them. You can especially experience these walls in the Golden Horn area where they’re pierced by a score of gates and posterns, many of them famous in the history of the city. Of these only one or two remain, although the location of the others can easily be determined, since the streets of the modern town still converge to where these ancient gates once opened, following the same routes they have for many centuries past. These gates open to many neighbourhoods in which they have given their names to such as Yenikapı, Edirnekapı and Kumkapı (with ‘kapı’ meaning ‘door’).
I have seen a variety of ancient city walls but Theodosios Walls are the best by far. It would be one of my top sites to visit as a local.