Circa 2nd Century A.D. Deep blue-green in color, the large twenty-sided die incised with a distinct symbol on each of its faces

“Several polyhedra in various materials with similar symbols are known from the Roman period. Modern scholarship has not yet established the game for which these dice were used.”
http://www.christies.com/LotFinder/search/LOTDETAIL.ASP?intObjectID=4205385
I guess it’s true what they say – no original ideas.