After capturing the city in 342 BC, Philip II undertook the construction of solid defensive walls. The very first of them were constructed in Cyclopean masonry technique with syenite solid blocks laid dry. The ancient citizens were able to reach Maritsa river through the steep stairs hewn into the rocks of the northern slope of Nebet Tepe (The Hill of the Sentinel). These stairs are still to be seen today.
A fragment of the fortification wall can be seen just to the North of the sfendona of the Stadium.