The 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. Some fortresses and towers were built to guard the walls, In the late 19th century the Ottomans destroyed most of the wall and towers. 

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