The site of the sanctuary of Ribemont-sur-Ancre (Somme, France) is of major scientific interest for the knowledge of the Celtic civilization in Europe. It also presents other peculiarities: two clearly identifiable periods of occupation-the first one as early as third century BC-to the second century AD and the second one from 1914-1918. In the area disrupted through military operations, the remains of several epochs are intermingled. In order to obtain a precise knowledge of the space time organisation of each occupation, a magnetic survey was carried out. The comparison of geophysical results with the aerial photographs shot during the war allows an exact determination of the origin of the anomalies. It becomes possible to separate the magnetic anomalies which are contemporary, anterior or probably posterior to the conflict of 1914-1918. The range of magnitude and the sign of polarity of anomalies appear as a means to facilitate the identification of the features of each period. Among the anomalies detected, some of them, such an the elliptic enclosure, have been identified by the excavations as unknown archaeological remains. Generally speaking, the ability of the magnetic method for surveying any structure in such a disrupted environment suggests a more frequent use in prospecting of the sites which were battlefields in Historic periods.