Roman military forts were enclosed by defensive walls or palisades that could vary widely in overall size, thickness and height depending on the fort’s purpose and local terrain. These fortifications were typically built from locally available materials such as earth and turf, timber, stone, brick and concrete, often combining several of these to create sturdy ramparts. The enclosed areas ranged from very small outposts housing only a few soldiers—sometimes less than 1 hectare—to large legionary fortresses that could cover 20–50 hectares or more.
Despite the modest size of the 1,53 ha enclosed area for the Maastricht castellum, these stone walls offered crucial protection in a time of crisis and uncertainty. They safeguarded the local population, civilian and military travellers and the agricultural surplus of the region, which was increasingly vulnerable to small-scale raids by Frankish raiders who occasionally breached the Rhinish limes frontier defences.