Thumbs Up Thumbs Down ?
Juvenal refers to the Roman custom of spectators’ voting on the fate of wounded gladiators with their thumbs. You may think a gladiator would appreciate the crowd’s “thumbs up” (verso pollice), but exactly the opposite is true. "Where we give thumbs up as a sign of approval, it meant death to its Roman recipient; much to the crowd’s delight".
In Rome audience participation often determined whether a competitor lived or died. The crowd decided by booing or cheering the wounded gladiator by yelling 'missum' or 'mitte' (release or send away) as a gesture of mercy and conversely yelling 'iugula' (to kill).
However the final decision in this was not made by popular crowd appeal and was usually left to a single judge
Thumbs down, signified “swords down,” which meant the loser was worth more to them alive than dead, and he was spared apparently so he could make up for his disgrace the next time he appeared in the arena.
Our reverse interpretation of this custom apparently was the result of the work of the French artist Léon Gérôme who apparently understood the Latin verso (“turned”) to mean “turned down”, and therefore in his painting Pollice Verso (1873) he presents the death sentence with the thumbs-down gesture. The painting became so popular that Gérôme’s mistake became the accepted interpretation and it is unlikely that it will ever be changed back to the meaning that it had with the Romans.
before Gérôme gave support to the view that “thumbs down” among the
Romans, meant the hapless gladiator was to be spared, not slain. The
gesture meant “Throw your sword down”. A 1601 translation of Pliny equates
the gesture with “assent” or “favor”, and John Dryden’s 1693 version of
Juvenal’s Satires gives the thumb being bent back,
not down, as the death signal. Some other written accounts of gladiator
matches say that pollicem vertere (“to turn the thumb”) meant kill and
pollicem premere (“to press the thumb”) meant spare..
Keep this in mind the next time you give someone the “thumbs up” sign.