This paper summarizes the principal geophysical results obtained at a recently discovered Roman city at Navarre. Prior to the survey, the extent of the affected areas and the characteristics of the settlement were unknown. The authors describe the field strategy applied and focus their discussion on the archaeological interpretation of the fluxgate gradiometer data. The results allowed for a detailed description of the layout in the main area revealing a city organized along the Roman road, which would have preceded the buildings. On the contrary, the results show important differences in magnetic contrast in the surveyed areas. Whilst the walls of the main area are well resolved, other areas do not show a discernible magnetic contrast even though their existence has been proven by other sources. The origin of these differences is discussed and preliminarily attributed to waterlogging or to differences in the thickness of the archaeological deposits. The magnetic survey, therefore, has shown itself to be a suitable technique for obtaining a preliminary assessment of the archaeological characteristics of the settlement, but cannot be used to definitively assess the affected areas. The results allowed zoning based on the contrast differences that will be used to guide further investigations. Copyright © 2016 John Wiley & Sons, Ltd.