The case study presented is a prime example of integrated geophysical–archaeological prospection. The aerial photographs available are complemented by non–destructive geomagnetic and geoelectric surveys with a reading distance of 0.5 m or less. To gain depth information and provide higher resolution, ground–penetrating radar (GPR) data are integrated. The GPR data were collected in a 0.5 $times$ 0.05 m raster and visualized as black–and–white time or depth slices. The developments presented allow us to incorporate GPR into the standardized interpretation process of archaeological prospection based on a geographical information system (Grs). Using GPR and all the other prospection data available as a basis, a detailed three–dimensional interpretation model of the monument detected, the southern part of the forum of the civil town of Roman Carnuntum, is created.