What was the original meaning of a thumbs up?

 The gladiator must die. In ancient Rome the original meaning of a thumbs up was that the emperor was ordering the death of a defeated gladiator.

 According to popular belief Roman spectators in the arena or Colosseum gave a thumbs down when demanding the death of a fallen gladiator. A Roman emperor's answer to this would then be a thumbs down of his own authorizing the execution. this, however, is a myth.

 The truth is the Romans did not use a thumbs down sign at all. When death was ordered, the emperor's thumb was stuck up in the manner of a drawn sword. When the loser’s life was to be spared, the thumb was tucked away inside the closed fist signaling for the winner to sheathe his sword weapon.

 In Latin the expression "pollice compresso favor iudicabatur" means "goodwill is decided by the thumb being kept in".

 Rumor has it that Ridley Scott, before agreeing to direct the movie Gladiator, viewed the painting Pollice Verso by the 19th century artist Jean-Léon Gérôme. The painting shows as a gladiator waits while the Roman emperor turns his thumb down to order his death. Scott is said to have been so captivated by this image that he immediately decided to direct the film.

 The only problem is the source of his inspiration was utterly wrong. Gérôme's painting is hands down responsible for one of the biggest fallacies of the 20th century, that is to say that thumbs down signaled death.

 According to most historians the artist wrongly assumed the Latin "pollice verso" - "turned thumb" - meant "turned down" when in truth it meant "turned up."

More proof that thumbs up means death

 If this weren't proof enough, the Roman medallion of the 2nd or 3rd century A.D. that was found in southern France in 1997 depicts two gladiators at the decisive moment and a referee pressing his thumb against a closed fist. The inscription on the medallion reads: "Those standing should be released."

 The use of thumbs up signs can still be easily misinterpreted in today's world. In Russia, the Middle East, and South America, a thumbs up is seen as a very rude insult, similar to the Western V-sign. This has caused several problems in Iraq, where American soldiers cannot be sure whether locals are welcoming them or are ready to blow them up.

 According to Desmond Morris, author of The Naked Ape, the positive connotations of the thumbs up in Britain can be traced back to the Middle Ages, where the sign indicated the closure of successful business deals.

 Thumbs up found a new lease on life when in World War II U.S. Air Force pilots used it as a signal to ground crews before taking off.

 When Ridley Scott was informed about the thumbs down fallacy, he still felt it best to have Emperor Commodus give the thumbs up when sparing Maximus, in order not to confuse the audience.