A large-scale resistivity imaging survey was performed in the acropolis area of Archaic Cnidos, south-western Turkey. This survey was a part of the geophysical studies conducted between 1999 and 2004. Two-dimensional resistivity data were acquired along a number of parallel lines using a pole-pole array. The data was processed using a 3D inversion algorithm based on a robust technique. We also applied shaded-relief processing to enhance the representation of the images of apparent-resistivity data and inversion results. In addition, the inverted resistivity data were visualized by a volumetric representation technique to display both the horizontal and the vertical extents of the archaeological structures. The inversion results revealed that a rectangular gridding pattern and a dense structuring existed in the depth range 0.35-1.5 m in the acropolis. Moreover, the bedrock was the base of the archaeological structures in the area. Based on the resistivity survey, four test excavations were carried out in various localities in the acropolis in 2004. These excavations yielded results supporting those obtained by the resistivity inversion. This indicated that large-scale 3D resistivity imaging can be a useful tool in archaeological prospection.