Together they're the biggest on-screen couple since Bogey and Bacall or Hepburn and Tracy. Each of them is easily worth $20 million a picture. Either would cause a civil riot if they walked down your street. It's a duo so mighty that no rival studio is willing to open anything against the debut weekend of The Mexican.

While this is indeed the sweetest, sexiest, brightest and most-anticipated big screen coupling in recent movie history - it's not like The Mexican is out to franchise Julia Roberts and Brad Pitt as the next big romantic duo.

They're really not on-screen together as much as you'd think. There's a little smooching. In a way, The Mexican is like three movies in one: A Brad and Julia modern romantic comedy, a Brad Pitt action-comedy and a Julia Roberts comedy-drama. Pitt plays a reluctant mob bagman. Roberts plays his girlfriend, who's ordered him to quit his life of crime.

Throw in prime-time's godfather (James Gandolfini from The Sopranos) as a gay hitman who takes Roberts hostage, and this picture would open even if it was in black-and-white, with subtitles, and played backwards.

But still, when they have their pick of projects, why would Hollywood's prom king and queen go south to make a dirty, small-budget road movie?

ENow's Christine Diakos asked Pitt if there was a certain promise a filmmaker has to offer to lure him to a project.

Well it first comes down to the character -- is there something there that is interesting, Pitt said. To me it was playing the chump, playing the anti-McQueen, the guy that is just not cool ... whatsoever.

Then, Pitt said, he had some good laughs when he first sat down with director Gore Verbinski. And then he considered casting. So it starts with the

writing, and the director and then who else is doing it, Pitt said. This kind of ensemble, with Julia and James Gandolfini leading the way ... it's just perfect and it came out of nowhere.

Pitt said the deal to do the movie came up quickly - within a couple of weeks of being approached, he was down in Mexico shooting the movie, and it was completed in six weeks.

Roberts' involvement was also negotiated swiftly and sweetly. She read the script, liked it, and met the director.

We sat down to have a conversation and he was very nice, Roberts told eNow. And I said, 'well you know, because I have sat in a room with a very nice director who gives all the right answers and then that guy never seems to make it to the set'.

As a test, she asked Verbinski to tell her the story of the movie, even though she'd already read the script. She wanted to get a feel for how he perceived the characters. And he told me a story that was so beautiful and so romantic and sweeping that I was almost in tears at the end, Roberts recalled. So I said 'if that's the movie you want to go off and make then I'll go off and make that movie with you'.

INDIE ACTION

The Mexican was a risk for Roberts, who is probably the only female movie star considered to be box office gold. This is her third time being nominated for an Academy Award and this year, she has a very good chance of picking up the big prize for Erin Brokovich. Ever since her first Oscar nod a decade ago on Steel Magnolias, she's worked her way up the Hollywood studio system with singular determination, and has never been known to flirt outside the mainstream or work on indie flicks.

Pitt, on the other hand, has been dabbling in indie films since the early 1990s in movies like Kalifornia, and more recently Fight Club and Snatch. In fact his biggest artistic failures have been in big budget movies like Meet Joe Black,

Seven Years in Tibet and The Devil's Own. In all three, Pitt played a brooding haunted man, undergoing some kind of emotional turmoil.

Lately, Pitt isn't taking acting so seriously and has been looking for roles that provided him - and the audience - with some fun. I've taken some lighter roles, he said. Not so deep, dark, dank and depressing.

And The Mexican fit the bill. This was so much fun, he said. We were sequestered away from the world in this little town, at the top of this mountain ranch. Staying in people's homes, using handheld cameras, we were gonzo shooting -- get up do a couple takes, move on to the next scene, and it was just great, great fun.

Even after this great experience, Pitt says it's still a mystery, what formula makes a movie work. Well you've got general rules, but my general rule is there are no rules, really. Because the minute you start answering to that the game changes. It has to evolve, it has to be part of an evolution.

Pitt and Roberts have both signed up to be part of the cast of Steven Soderbergh's next picture, a re-make of Ocean's Eleven. They join a cast of A-list actors - including Matt Damon and George Clooney -- taking a chance with yet another loose, indie-type film.

PRODUCTION NOTES:

Director Gore Verbinksi first envisioned The Mexican as a modest film with relative unknowns in the lead roles. However, who could say no to Brad Pitt and Julia Roberts? Verbinski began his career with a series of award-winning TV commercials, and his previous feature film was the inventive comedy Mouse Hunt, starring Nathan Lane. He describes The Mexican: At its heart the film is a romantic comedy ... but with a little bit of Sam Peckinpah.

Screenwriter and exec producer J.H. Wyman is a Canadian ex-pat, a former actor who appeared on shows like Highlander and Lonesome Dove: The Outlaw Years. This is his first screenplay to be produced, one full of unpredictable twists and turns, both on screen and off. As for the plot twists in the story, Wyman says: Nothing happens as you would think.