> Sort of like when the Caesar in _Gladiator_ signals an execution in the Colliseum with a thumbs-down sign--EVERY historian knows that was always signaled thumbs-up, but this wouldn't make sense to a modern movie audience, so it was changed to reflect the current connotation, rather than the original.

I thought that there was argument about this amongst historians, so I had a quick look in the Interweb, and the closest I can come to a consensus is that neither gesture was much like the modern "thumbs up" or "thumbs down".

"The [referee's] gesture signifying that the gladiator should be killed is not exactly thumbs down, but thumbs turned. Christopher S. MacKay says the thumb motion represents the plying of a sword." seems to roughly sum up modern thinking on the issue.