According to this report, Jelmer Eerkens (UC Davis) and Alex de Voogt (American Museum of Natural History) assembled and analyzed a set of 110 carefully dated, cube-shaped dice and made the following main findings (their full paper is available here):
• Dice made before 400, or in Roman times, are highly variable in shape, size, material and configuration of numbers.
• Dice are very rare between 400 and 1100, corresponding to the Dark Ages.
• When dice reappear around 1100 they are predominantly in the “primes” configuration, where opposite numbers tally to prime numbers (1-2; 3-4; 5-6), a numbering style that was also popular in ancient Mesopotamia and Egypt. Early medieval dice also tend to be quite small relative to their Roman predecessors.
• Around 1450 the numbering system quickly changed to “sevens” where opposite sides add up to seven (6-1; 5-2; 3-4). Dice also became highly standardized in shape, and also were made larger again.