Reverse Engineering the Roman Dodecahedron: Mechanical Reconstruction of a Gallo-Roman Coin Sorter and Wearable Vault

The Gallo-Roman dodecahedron (2nd to 4th century CE) has remained one of archaeology's most enduring unsolved mysteries for over 250 years. Previous hypotheses classifying the bronze artifact as an astronomical instrument, a cult object, or an optical rangefinder fail due to the lack of standardization, historical currency contexts, and severe mechanical contradictions. In this paper, the object is comprehensively deconstructed for the first time through rigorous reverse engineering and experimental archaeology, utilizing the principles of mechanical engineering and ancient product design. A mathematical reassessment of archaeological raw data (using the Jublains artifact as a primary reference) refutes the assumption of isolated optical sightlines. Instead, geometric analysis reveals a C5 rotational symmetry with precisely mirrored hemispheres, a continuous oval polar axis (acting as an intake and output chute), and the reduction of the openings to exactly three standardized size classes. The widely debated asymmetric dimensional tolerances (ovality) of the holes are identified not as casting errors, but as a mandatory feature of a mechanical go/no-go gauge. This asymmetry enabled the flawless volume verification of irregularly hand-struck ancient coins (al-marco minting process). Furthermore, physical reconstruction reveals the dodecahedron as the rigid, shape-giving exoskeleton of a modular leather system. The 20 corner knobs functioned neither as decorative elements nor as stand feet, but as mechanical anchor points for a custom-fitted receptacle made of wet-molded leather and a shock-absorbing pentagram lacing. The reverse engineering proves the existence of a highly functional 2-in-1 multi-tool designed for the harsh realities of Gallo-Roman commerce: An opaque, belt-worn travel vault (everyday carry) that, due to its weight and bundled top-lacing, could be instantly deployed as a formidable self-defense weapon (slungshot / morning star) in emergencies. A mechanical drop-safe cash register that, by folding the leather casing down into the equatorial knob ring, transformed into an error-proof coin sorting funnel (poka-yoke) with an integrated collection bag to secure market transactions. This paper demystifies the artifact, removing it from the realm of mystical speculation and repositioning it as a pragmatic masterpiece of functional, ancient industrial design.