One of the main forms of expression of the power of the Dacian Kingdom, with its capital at Sarmizegetusa Regia, was represented by the monumental constructions built in ashlar stone, the result of a mixture between local traditions and Greek and Roman influences. The fortified acropolis at Piatra Roșie is one of the main components of this center of power and one of the most important archaeological sites from the Late Iron Age in Romania. In 1999 it was inscribed on the World Heritage List as part of the serial site “Dacian Fortresses in the Orăștie Mountains”. This paper presents the most recent data regarding the stones used in the construction of the Piatra Roșie fortress, the most important building material from the point of view of volume and durability. The historiographical and archaeological data, the field investigations and measurements, together with the mineralogical analysis of stone varieties have been corroborated with specific interpretations for construction engineering and 3D modeling applied in the evaluation of the dimension stone volume. The present approach constitutes an absolute novelty for the site of Piatra Roșie, and, also, a model that can be applied to the specific conditions of the other Dacian Fortresses.