The thumbs-up/thumbs-down gestures which stem from gladiatorial events had different if not opposite meanings to what they do today. A down-turned thumb by an official symbolized the winner burying his sword in the sand and the loser's life spared; an upturned thumb expressed delivering the killing stroke, symbolizing a slit throat. The actual gesture remains unknown - our belief in the thumbs-up/down stem from a painting by Gerome (pollice verso - with turned thumb) the surviving descriptions 'Infesto pollice' (with hostile thumb) and 'pollice premere' (with thumb pressed down) are too ambiguous to conclusively state what gesture was used in reality.
Kit Harington suffered from body dysmorphia (excessive anxiety about the appearance of one's body) while working out for this role. He said he became completely obsessed with it to the point where he was "going to the gym three times a day for six days a week." He suffered from a case of "exhaustion" and eventually his trainer stepped in to rein him in. But he said that he was "proud of what he achieved in the end".
Director Paul W.S. Anderson said that he was not pleased when a lot of people online said that Kit Harington's six pack abs were digitally enhanced and not real after the first stills and trailers for the movie were released. He reiterated that they were completely real with no make-up or digital enhancement and Harington actually looked like that for the shooting of those scenes.
Leading man Kit Harington underwent an extreme physical transformation for the film at his own behest. After he read the script, he went up to director Paul W.S. Anderson and told him that to portray the character as written in the script (his character Milo is described as "absolutely ripped"), he would transform his physique completely. Consequently, Kit Harington undertook a heavy 'bulking' regimen and a diet of 3000 calories a day to put on 2 stones (12.7kg/28lbs) of weight in 5 weeks. He then went on a very severe diet and 'cutting' regimen for 4 weeks to cut back from 12 stone (76.2kg/168lbs) to 10 stone (63.5kg/140lbs) acquiring intense muscle definition in the process. Harington later said that he was very pleased with the results and that it was the best shape of his life.
Kit Harington's shirtless introduction scene (in the gladiatorial arena in London) was shot on the last 2 days of principal photography to give him as much time as possible to get his body in shape. He started training before filming began and throughout filming to peak for that scene.
Paul W.S. Anderson said that he re-shot the scene after whipping of Kit Harington's character where he and Adewale Akinnuoye-Agbaje have a conversation while being shirtless because towards the end of the filming he realized that they had gotten "way more cut" than when they had filmed it.
Kit Harington said that he always wanted to do a complete body-transformation for a role. This was the primary reason for his accepting this role. Another reason was that it gave him his first shot at being a macho leading man, something he always wanted to do.
Kit Harington's gladiator costume for his introductory scene was almost scrapped. It was specially designed to show Harington's abs, but they weren't quite ready before filming began. The sequence was postponed to give Harington more time to prepare. Eventually, he was able to get his abs in shape and pull off the revealing costume.
Nuno Capitao de Salles, Kit Harington's personal trainer, revealed that during the filming of Harington's shirtless scenes, he would stand just outside the view of the camera and yell at Harington, "Contract your abs" or "Flex your abs" to keep reminding Harington to flex his abs for the shot.
The trivia item below may give away important plot points.
In reality, among the ash-covered bodies buried by the volcano, archaeologists did find two people actually embracing together (although not in the position depicted in the movie), and they are now known as "The Lovers of Pompeii". At first thought to be a young couple and later two members of the same family, recent DNA studies have shown the "lovers" to both be young men in their late teens/ early twenties and not related to each other. Also, the corpse of a very large man, probably from North Africa, was really found in Pompeii's arena.