The Acropolis walls, built to defend the city in the early Byzantine period (around 390 AD), were 7 kilometers long, 5 meters thick, and 10 meters high. In addition, some fortresses and towers were built to guard the walls. In the late 19th century, the Ottomans destroyed most of the walls and buildings.

The Trigoniou Tower is the most famous and impressive tower on the wall. It was built in the late 15th century to prevent an invasion of the city and help during a siege.