From the 5th century BC on, the city of Kavala was surrounded by a protecting wall. This was repeatedly modified over time - according to sources, extensive modifications and repairs were carried out after the Roman period by Emperor Julian between 361 and 363, then by Justinian , and again in 926 by Basil Cladon, general of the Theme of Strymon. That being said, the Byzantine wall probably owes its present form to Andronicus II Palaeologus, who combined the fortifications with the city's water supply, following the earlier model applied by Justinian to Anastasioupoli. Τhe fortifications appear to have been rebuilt and modified throughout the Byzantine period, with a new external defensive wall being added to the city’s defences in the 16^th century; the northeast section of this is still standing.

Following the lie of the land, the defensive wall girdled the hill, encompassing an area of ​​13 hectares. The enclosure was reinforced by round and square towers and bastions, mainly on the most vulnerable land side to the north. The perimeter is closed off by a transverse wall 449 metres in length, which climbs a steep slope to the most inaccessible cliffs on the north side to a height of 64 metres. The wall had four gates to facilitate movement into and out of the city. As part of the rebuilding projects carried out to reinforce the city’s defences, the citadel of Byzantine and Ottoman times was built on the hilltop site of its ancient counterpart.

The irregularly shaped citadel fortifications include the northern part of the city’s defensive walls, reinforced by two square towers on each of the northwest and northeast corners, a polygonal tower on the east side and a bastion on the southeast. The area inside the citadel is divided in two by a transverse wall running northwest - southeast, crowned at the central, highest point by a cylindrical tower.

The city’s defences also included a 1.5 km long wall, which written sources attribute to Andronicus II Palaeologus, between 1307 and1308. It was built on the occasion of an unsuccessful attempt by the Catalans to conquer Kavala, and was primarily used to control the road leading from Macedonia to Thrace via the city. This cross fortification began on the north side of the city walls and led to the opposite hills, interrupted only by the aqueduct. It ended in three square towers and one round one.