[yetanotherloser]

Board games are much older than the Romans, though possibly not older than writing - and texts give us a bit of a clue that some early ones were part recreation part ceremonial. By Roman times pure recreational games were common and reasonably often referenced in their literature. They definitely used cubic dice with numbers on for games (and gambling). The icosahedral dice usually have Greek letters rather than numbers (occasionally symbols IIRC) which make them hard to move a piece to or compare scores; we don't seem to find them with game boards like we do "Latrunculi" counters; there's no textual support for a game with them (weak evidence, true) but there's a fair bit for strong interest in divination and oracles that could use them. So not a dead cert, but fairly likely for the D20s. Whereas when you find a Roman D6, you can be pretty sure it's for gaming and/or betting (or a thief's hit points).

[tessierashpool]

Greek letters were used as numbers during the time of the Romans.

https://en.wikipedia.org/wiki/Greek_numerals

also, sorry to be that guy, but D&D hasn't had a thief class since 3rd edition came out, in 2000.

[dukeyukey]

To be fair there's a Thief subclass

[yetanotherloser]

re: being That Guy: I know. It's a weak "Romans were old school" joke.

[yetanotherloser]

ps good shout on the letters, which I had thoroughly forgotten. The d20s still are odd though.