The naturally fortified location of Ambracia was reinforced by massive and imposing walls, 4.5 km in length, which in their most part followed the course of Arachthos river. The city needed protection not only from enemies but also from the frequent river floods. Sections of the walls have remained visible throughout the centuries in many parts of the modern city such as those at the lower part of the Byzantine castle, while many other parts have come to light by the salvage excavations carried out in the last decades. The walls, constructed from local white limestone, have a thickness of 3.5 -5.60 m and consist of two sides with a filling between them. At various points they were bolstered by strong semicircular or rectangular towers.