This exhibition deals with the emergence and organization of the Middle Byzantine fortress. The former was the result of a series of events (raids, epidemics and earthquakes) and their consequent economic crises, which brought on the gradual shrinking or abandonment of most Early Christian cities in the seventh and eighth centuries AD.

These fortresses, or fortified settlements, were built at defensible locations to control nearby roads and provide security for their inhabitants and those of the surrounding area in times of war. They provided the basic functions of an urban centre, but their confinement and often uneven terrain affected urban planning and domestic architecture. The archaeological and instructive material, which is exhibited in the museum's sixth room, illustrates the layout and defense of a Byzantine fortress, its daily life and aspects of production in and around it. The exhibits come from various fortresses of Macedonia, particularly that of Rendina, which controlled the route leading from eastern to central Macedonia and had an important place in the region's ecclesiastical organization. The display includes a fifteen-minute video documentary on the fortresses of Macedonia and Thrace.