The Roman period Castrum Zerzevan is on a hill 35 km south of Diyarbakır, Türkiye. Various field evidence (e.g. petrographic similarities, sudden changes of the topographic contours, the morphology of the nearby hills, and traces of the on-site quarry activities) suggests that the topography of the hilltop was artificially modified and used as a quarry. This study aims to introduce an approach that creates the ancient topography and calculates and verifies the volume of the on-site material required to build the fortification and associated structures by applying morphological analyses. The primary objective of the methodology is to reconstruct the site’s ancient topography and examine the difference between its former and present surfaces. The result indicates that approximately 36% of the extracted material was used in the enclosure. The overall findings and site investigations suggest quarrying and construction activities were carried out in a planned manner or concurrently at the site. In addition to the collected samples’ petrographic and geochemical similarities, the Castrum‘s topographical modifications and the suitability of the geological unit as a building material support our claim that the Romans were well aware of environmental conditions (including topography and morphology) and material performance.