As part of a restoration project for the ‘Porte de Mars’ in Reims, an archaeological intervention in several phases took place. The first phase consisted of an excavation at the foot of the building, covering its entire perimeter. The second phase was linked to the dismantling of the concrete roofing installed in the 19th century; this enabled the upper part of the building to be examined and the construction method used in the inner part of the piers to be determined. The last stage will allow the archaeological, architectural, stylistic and geological study of the building to be resumed, in particular to specify the method of construction of the monument and the stones used, to analyse its decoration and to highlight the various restorations already carried out. It also permits all the data acquired to be synthesised, first in a 3D model, and subsequently in a GIS containing all the information about the monument.