Although the powerful centralized authority of the Macedonian kings ensured peace within their dominions, all the cities of the kingdom were walled to withstand the frequent barbarian incursions. Making the best use of the terrain, they combined natural and man-made fortifications.
The cities with their 'acropoleis' (citadels) (e.g. Aigai, Thessalonike) were encircled by walls built of equal courses of stone slabs in straight lines surmounted by unbaked bricks or, more rarely, masonry, and reinforced at intervals with rectangular or round towers (Olynthos).
The number and position of the gates was determined by the disposition of the terrain and the road network (Philippi, Amphipolis), while ditches with embankments were used for the collection of rainwater (Dion).
In the Hellenistic and Roman periods, the evolution of siege techniques and the use of siege machinery led to a gradual change in the design of walls (Thessalonike), improved placing of the gates, and the reinforcement of towers.