Zack Snyder's fantasy take on one of the most famous battles of ancient history may have angered the classicists but, as Steve Pratt reports, it's certainly pleasing the punters.

It's the $64,000 question but not one that director Zack Snyder can answer. A much bigger amount of dollars - 71 million, to be precise - are the reason for asking. That figure was the first weekend US box-office take of 300, a movie like no other you've ever seen.

To the surprise of everyone, not least director and co-writer Snyder, the film's opening collected more money in ticket sales than the $60m it cost to make this visually startling retelling of 300 Spartans taking on the massive Persian army at the Battle of Thermopylae in 480 BC.

So why has it done so well? "I have no idea," admits Snyder, who made his directorial debut on the horror remake, Dawn Of The Dead.

"The truth is we made a $60m film which, in Hollywood terms, isn't a ton of money and it's a very genre specific movie. You take Frank Miller's graphic novel, which is very particular, and his aesthetic, which is pretty radical, and make a movie that's consistent with his vision - and that's something slightly original in the movie world. Maybe that's it.

"Perhaps when they look at the trailer, people go 'I don't feel the cold hand of Hollywood on me'. I wanted to give people an excuse to go to the movie theatre because I feel like cinema, or the going-to-the-movies experience, is in danger in the world right now. People have 50ins plasmas at home and surround sound, I mean, really, why venture out?

"This is a movie that, if you see it in a crowded cinema with a bunch of knuckleheads, is pretty cool."

Graphic novelist Miller's Sin City was brought to the screen a few years back with some success. 300 is different because of its historical basis in the story of the handful of Spartans, led by King Leonidas, who took on the entire Persian army.

Although Miller's interest in the Battle of Thermopylae was triggered by seeing the old Hollywood movie, The 300 Spartans, as a child, his graphic novel approach couldn't be more different.

And the film is similarly unconventional. 300 was shot almost entirely in the studio against a blue screen so that backgrounds and effects could be added later. The dialogue has a classical feel, while the action is a shocking mixture of blood spurting, limbs being hacked off and soldiers mutilated as the original visual style, almost cartoon-like, gives the battle scenes a dreamlike quality.

No wonder it has taken five years to put 300 on the big screen. "I had my first meeting with him in 2002 and he wrote the book in 1996, so it's been around for a little while," says Snyder.

"In the graphic novel world, 300 is considered as pretty obscure. It was a passion project for him. He fell in love with the original movie and the idea that heroes die was revolutionary to him. It's plagued him all his life, there's always a tragic kind of hero in his stories. He repeats it over and over. It's not a particular thing to 300, it's in all his work."

He attributes getting to Miller at the right time for securing the rights from him to make the film. "He was busy on Sin City when I came up with this idea, he was just surfing with that wave. He thought maybe Hollywood would redeem itself for him as he was pretty fed up. Hollywood had come calling and then beat him up," he says.

"The entire time we talked about 300, I really didn't think the movie was ever going to get made. Originally I went to the studio with the graphic novel and said 'okay, this is the movie'. They came back and said they needed a script. All I had was the comic book. They didn't like that at all."

Historians have taken the movie to task for not being accurate. Snyder makes no apologies for his take on the battle and its leading players. Yes, he did a lot of research, but did he put it in the movie? "Not really," he says. "Frank had gone to Thermopylae and put his hands in the dirt, and turned the whole thing into his own mythology.

"We changed things at first, then realised if you pull out one pin, the whole thing collapses. This is Frank's mythologised version. For instance, there are no reports anywhere of elephants at Thermopylae, but he put them in the book."

Having decided not to render the reality, he felt it his responsibility to push the film even further into fantasy to ensure no one would take this as an accurate depiction of people and events.

"I did whatever I could think of to make it a fantasy. I feel it's closer to Pirates Of The Caribbean than to Alexander. To me, it's a complete fantasy although it's grounded in historical terms," he says.

This hasn't stopped the film being criticised for its depiction of ethnic groups or seemingly making the Persian ruler Xerxes homosexual. But then Xerxes wasn't 8ft tall, as he is in the movie, and almost certainly didn't wear a sparkly jockstrap.

"Even the way the Spartans are represented in the movie is completely crazy. So the criticism is surprising to me. People will see the movie and take from it want they want, but the last thing I intended was for the movie to be offensive to anybody and I'm deeply sorry if they feel that way," says Snyder.

"I thought that if I pushed the film towards fantasy, people would see the intention was a cinematic romp. I hope as more people see the film they will realise that physical reality doesn't apply."

He'd reckoned without some taking the whole enterprise far too seriously. 300 is a gloriously entertaining camp movie that I would call a costume drama if the Spartans wore more than little leather knickers and capes. Still, they only want to show off their six-packs. There are more on display than in a brewery warehouse, the result of an intensive diet and exercise regime for the cast led by Gerard Butler as Leonidas.

The biggest challenge for Snyder wasn't getting fit but the schedule. He had to shoot the entire film in 60 days which, for one featuring big battle scenes, was pretty ridiculous. "I was adamant about making the fights particular and sort of beautiful in their own way. That's time consuming. We were constantly battling the schedule," he says.

Many of the cast are from this side of the Atlantic. Female star Lena Headley jokes it was because English actors are cheap. But Snyder had an ulterior motive. "This is going to sound ridiculous, but I knew the movie was going to look so weird but if the actors had English accents it was a convention that people were used to - English accents in ancient films," he explains.

"And they're more classically trained than other actors. The blue screen environment is rather like a stage, the performances are coming from another actor, not the world they are in."

300 (15) opens in cinemas on Thursday.