A Handheld Lunar Dioptron? A Functional Reconstruction of the Gallo-Roman Dodecahedron

This preprint proposes a new functional reconstruction of the Gallo-Roman bronze dodecahedron as a compact handheld astronomical dioptron, potentially used for observing the relative position of the Moon and nearby planets or bright stars. In the proposed model, one of the vertex knobs acts as an occulting stop for the bright lunar disc, while the opposite vertex helps stabilize the line of sight. The perforated faces of different diameters provide a set of discrete viewing windows around the occulted Moon. The concentric rings are interpreted cautiously as possible centering and identification marks rather than as a universal numerical scale. The reconstruction is based on historically attested principles of ancient dioptric observation associated with Hipparchus, Ptolemy, Heron of Alexandria and Pappus, including sighting through apertures, occulting bright celestial discs with opaque elements, and measuring angular relationships between celestial bodies. This proposal differs from the 2012 dioptron hypothesis of Amelia Carolina Sparavigna, which interpreted the dodecahedron primarily as a terrestrial rangefinding instrument. The present reconstruction instead proposes an astronomical application, with the Moon as a possible reference object and with a potential connection between practical observation and ritual, cosmological or divinatory use. The hypothesis does not claim that the function of the Gallo-Roman dodecahedron has been definitively proven. It is presented as a testable functional reconstruction intended to explain several characteristic features within one operational model: the hollow body, differently sized perforations, twenty vertex knobs, opposing geometrical axes, possible mounting on a short handle, and concentric markings around the apertures.