Digital approaches to ancient metrology: new insights into methods and tools for measuring and designing marble in late antiquity

The paper deals with a particular category of production indicators, namely circular holes on Late Antique architectural sculpture. The Mediterranean-wide distribution of these graphic signs suggests that they had a defined meaning and function during the production process. A sample of marble objects from Late Antique Ravenna has been 3D digitally survey and analysed here as a case study. A comparative assessment of these marks suggests their identification as calliper holes. The evaluation of their positioning on the marble objects provides precise clues to their function for metrological and design purposes. Moreover, it points to a specific production technique used during manufacture, namely the three-compass method. The chronological distribution of archaeological evidence between the 5th and 6th centuries AD makes it possible to link the phenomenon to the floruit of the quarries of Proconnesus and the introduction of new techniques to speed up marble working.