Even before the screen adaptation, Chicago was one of the most successful musicals in Broadway history. Holding the record for the longest-running musical on Broadway, as well as that for the longest-running American musical on the West End, the story of two vaudevillian villains and their journey to freedom is just as compelling now as it was back in 1975. When the screen adaptation was released in 2002 it gained its own reputation as a must-see, winning the Academy Award for Best Picture that year along with five other awards.

Now, over 15 years after its original release, it still stands tall as one of the best screen musicals to ever be released. All of the core cast speak of it fondly, explaining that the movie did so well because the atmosphere on set was so fun and relaxed. There’s even talks of a reunion, with star Renee Zellweger in particular teasing that she’d love for the group to team up and play their old parts once again, whether on screen or on stage.

In honour of this murderous musical’s enduring legacy, we’re counting down the top 10 things you probably never knew about Chicago.

10. John C. Reilly is a secret clown expert

John C. Reilly’s character in Chicago is Amos Hart, the loyal but oblivious husband of Roxie Hart. His big musical number is Mr Cellophane, where he complains about the fact that he’s always being pushed aside and overshadowed. The song is done in a ‘tramp-clown style’, which involves wearing tattered clothing and a face of sad clown make-up.

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It might seem outlandish and hard to relate to, but Reilly said it was the most comfortable character he had ever played. Not only did he understand the motivations, but he could do his own make-up and even choreograph his own steps, since he knew a lot about clown culture already and had even planned to go to clown college after school.

9. Only one actor was snubbed by the Oscars

The year Chicago was released it was nominated for 12 Academy Awards, including several nods to the main cast. Renée Zellweger was nominated for Best Actress, John C. Reilly was nominated for Best Supporting Actor and Catherine Zeta-Jones and Queen Latifah were both nominated for Best Supporting Actress.

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In fact, the only actor with a large role in the movie who wasn’t nominated was Richard Gere, who received no recognition for his take on the character of Billy Flynn. Gere was reportedly genuinely upset by the oversight, saying he was waiting for his name to be read out and was shocked when it wasn’t.

8. It’s based on a true story

The story of two glamorous girls getting away with murder in the same year might seem unlikely, but it’s actually based on stone cold fact. In 1924, Beulah Annan (the inspiration for Roxie Hart) and Belva Gaertner (the inspiration for Velma Kelly) both made headlines in Chicago, later becoming known as the Jazz Baby Murderesses.

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Just like in the movie, both walked free, and were fawned over by journalists for their glamour and mystery. In fact, it was a journalist who covered the trials who went on to write the first play based on the events, though she was much more cynical towards the two women than the majority of the press.

7. The part of Billy Flynn was impossible to fill

The part of Billy Flynn is one of the most fun roles in theatre, but it’s also one of the most demanding. Actors must be able to tackle not one but two major songs in the show, as well as tap-dancing and acting the whole time. Richard Gere’s performance is now synonymous with the role, but he wasn’t the director’s first choice to play the slimy but talented lawyer.

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Both Hugh Jackman and Jon Travolta were approached to play the part, and both turned it down, with Jackman saying he felt too young to play the part convincingly. By contrast, Travolta turned it down because he thought it was a story about women who hated men and, as he put it, he preferred stories about women who loved men. When both men saw the finished film, they both made it known in interviews that they regretted their decision.

6. Velma Kelly has a bob for a very specific reason

Catherine Zeta-Jones was enamoured with the role of fashionable murderess Velma Kelly, and she worked to master every step until she was black and blue wit bruises. Her dedication to the character paid off when she was awarded the Oscar for Best Supporting Actress, and she took no chances in making sure she was recognised for her hard work.

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For example, when one producer suggested the character have long hair, she shot down the idea and refused to budge. This is because she was worried people would see her hair blocking her face as she danced, and assume that she had a body double instead of doing the dancing herself.

5. There was a rivalry between the two stars

Chicago’s two main characters, Roxie Hart and Velma Kelly, spend the movie oscillating between cautious allies and bitter rivals. By contrast, Catherine Zeta-Jones and Renee Zellweger were fast friends throughout filming, with Zellweger even claiming that watching Zeta-Jones perform I Can’t Do It Alone was her favourite moment throughout the whole shooting process.

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With that said, even though the two were inseparable, behind the scenes their people were having a battle of their own. Nobody could decide which star deserved top billing over the other, leading to the names of both actresses appearing diagonally on most of the posters and promotional materials.

4. The studio had an odd request

Zeta-Jones and Zellweger both embodied their parts brilliantly, to the point where it’s difficult to imagine another star playing either Roxie Hart or Velma Kelly. With that said, another big name was almost cast as Roxie in particular, and the pick came directly from the head of the production company themselves.

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Nobody is quite sure why, but Harvey Weinstein was obsessed with the idea of Britney Spears playing Roxie Hart, and even sent three executives backstage at one of her shows to convince her. However, both the director and choreographer of the movie were staunchly against casting a bubbly young pop star to play such a dark role, and eventually the suggestion was dropped all together.

3. Beyonce wanted the part of Mama Morton

Speaking of pop stars, Britney Spears was not the only one interested in making an appearance in the film. Beyonce fell in love with the role of the stern matriarch and prison guide Mama Morton, whose role demanded a show stopping voice.

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Beyonce obviously had no shortage of vocal talent, but casting directors at the time were more focussed on Kathy Bates. When she dropped out of the running due to shooting conflicts with About Schmidt, the role passed onto Queen Latifah, another actress with a musical background. As for Beyonce, she got her acting opportunity when she starred in Dreamgirls just a few short years later.

2. The original Roxie was kicked off the project

Renee Zellweger was apparently so intimidated by the role of Roxie Hart that she couldn’t think more than a day of shooting ahead, and was constantly terrified of doing something wrong. Her fears were made even worse by the knowledge that another actress had been chosen to play Roxie before her, and that actress was Charlize Theron.

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Theron had signed on to play Roxie and had even begun rehearsing, but when the original director dropped out and was replaced, Theron went with him. The new director apparently just didn’t want to work with her, leading to a lot of regret regarding the project. She did make sure to congratulate Zellweger on her performance though, saying in interviews that she wasn’t sure even she could have done a better job.

1. Catherine Zeta-Jones was pregnant while filming

Shooting any film is an arduous process, and working on a musical is an even more daunting prospect. Along with lines to learn, there are full numbers to rehearse, with both steps and lyrics to learn by heart. It’s a physical challenge for any actor, but even more so when that actor is pregnant.

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Zeta-Jones got pregnant around two months before shooting began, but insisted on doing every step herself regardless. Even when she had to be shot from certain angles to keep her bump from being visible, she persevered with the choreography as it had been given to her, and even performed a full song-and-dance number from the movie live at the Oscars, just ten days before she gave birth.