The city was fortified from its establishment in the late 4th century BC, but the present walls date from the early Byzantine period, ca.

The walls consist of the typical late Roman mixed construction of ashlar masonry alternating with bands of brick.

The northern part of the walls adjoins the acropolis of the city, which formed a separate fortified enceinte, and within it lies another citadel, the Heptapyrgion (Seven Towers), popularly known by the Ottoman translation of the name, Yedi Kule.

[1] The first fortification of the newly built city of Cassander, which played an important role, dates back to the 3rd century BC.

At the beginning of the 4th century, Galerius and Constantine the Great passed through Thessaloniki and strengthened the walls.