A Roman dodecahedron is a small hollow object made of bronze or stone, with a dodecahedral shape: twelve flat pentagonal faces, each face having a circular hole of varying diameter in the middle, the holes connecting to the hollowed-out center. Roman dodecahedra date from the 2nd or 3rd centuries CE.
About a hundred of these dodecahedra have been found from Wales to Hungary and to the east of Italy, with most found in Germany and France. Ranging from 4 cm to 11 cm in size, they also vary in terms of textures. Most of them are made of bronze but some also seem to be made of stone. A Roman icosahedron (a polyhedron with twenty faces), has come to light after being misclassified as a dodecahedron and put away in a museum's basement.
No mention of them has been found in contemporary accounts or pictures of the time. Speculated uses include candlestick holders (wax was found inside two examples); dice; survey instruments; devices for determining the optimal sowing date for winter grain; gauges to calibrate water pipes or army standard bases. Use as a measuring instrument of any kind seems to be prohibited by the fact that the dodacahedrons were not standardised and come in many sizes and arrangements of their openings. It has also been suggested that they may have been religious artifacts of some kind. This latter speculation is based on the fact that most of the examples have been found in Gallo-Roman sites. Several dodecahedrons were found in coin hoards, providing evidence that their owners considered them valuable objects. Smaller dodecahedra with the same features (holes and knobs) and made from gold have been found in South-East Asia. They have been used for decorative purposes and the earliest items appear to be from the Roman epoch.
- The earliest finding is reported in 1739 and since then the count has mounted to 116 similar objects; Michael Guggenberger (2013), The Gallo-Roman Dodecahedron, The Mathematical Intelligencer , Vol. 35, Dec.2013, Iss. 4 , pp 56–60
- Sparavigna A., (2012) Roman Dodecahedron as dioptron: analysis of freely available data, Arxiv, 
- Wagemans G.M.C., The Roman Pentagon Dodecahedron, An Astronomic Measuring Instrument for Determining the optimal sowing date for winter grain ; this webpage also has a map of the distribution of the dodecahedra
- Henig, Martin (1984), Religion in Roman Britain, Routledge, p. 128, ISBN 0-7134-6047-4
- Kilford, L.J.P. (December 2004), "A Mathematical Tourist in Germany", Mathematics Today 40 (6): 204
- Bernhard A. Greiner: Römische Dodekaeder. Untersuchungen zur Typologie, Herstellung, Verbreitung und Funktion. In: Carnuntum Jahrbuch 1995 (1996) 9–44
- Anna T. N. Bennett, Gold in early Southeast Asia, ArcheoSciences, 33, 2009, 99-107; see also Xiong Zhaoming, The Hepu Han tombs and the maritime Silk Road of the Han Dynasty, Antiquity, Vol.88,Iss.342,Dec. 2014, p.1229-43
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- "History Mystery: Ancient Dodecahedron's Purpose Remains Secret" by Alexandria Hein, Fox News, June 10, 2011