The topic of military settlements and the role of troops in the northern provinces of North Africa during the age of the Roman Empire has recently gained a strong interest in historical, archaeological, epigraphical, and economic studies. In particular, at Mauretania Tingitana (in the north-east area of modern-day Morocco), the presence of numerous military camps in the Early and Later Roman Empire has now been assessed. In this framework, the present work deals with the geophysical survey, by means of magnetometry, at the site of el Benian, where the largest military camp is located. In particular, the magnetic survey has highlighted the organization of the camp, almost totally unknown previously. The result of the magnetic survey has confirmed intense building activity over the centuries and made it possible to identify and characterize the structures typical of a military field.