The Pirates of the Caribbean series is one of the most famous film sagas in the world, right up there with Star Wars and the Marvel Cinematic Universe—but it wasn’t always that way. When 2003’s The Curse of the Black Pearl was in its initial early planning stages, the writers had no idea they were about to reinvent an entire genre.

Black Pearl had a few roadblocks to sail over, one of which was its small budget. The film was made on a budget of $140 million, and those involved in production had no idea what a wild success they had on their hands, or that it would go on to gross $305.4 million. The film’s tiny budget meant CGI had to be kept to a minimum, so the villains—pirate Captain Barbossa (Geoffrey Rush) and his cursed skeletal crew—had to be rethought a bit. The Hollywood Reporter recently interviewed screenwriter Terry Rossio, who we can thank for introducing that story element into the script.

One funny moment came during story development, regarding the skeleton pirates in the moonlight. We knew we wanted to have sword-fighting skeletons from the start because those were cool and already part of the ride. But we also wanted to see the actor's faces, you don't want to make Geoffrey Rush into a skeleton for an entire film. So, the natural idea would be to do it like in Ladyhawke, pirates by day, skeletons by night.

But the producers shook their heads. With all the nighttime fight scenes, CGI was expensive at the time. We couldn't afford for the pirates to be skeletons all night long. I was sitting at the table and laughed out loud. Everyone looked at me. “What if the pirates are skeletons at night, but only when the moon comes out? Can we get away with that?” They loved it. “Yes! When the budget gets tight, we just put a cloud in front of the moon!” And that's what we did.

The first sequence in which you see the effects of the pirates’ curse, when the crew is dragging Elizabeth Swann (Keira Knightley) around the ship, looks fabulous even by today’s special effects standards. But even then, the writers were still uneasy about the project at times. The movie was coming after plenty of other swashbuckling adventure films of its kind. “We were certain we were writing the last pirate film that would ever be made,” Rossio said, so there was pressure to make their tale original.

“We knew that audiences would resist talking parrots, peg legs and other pirate tropes that are a bit goofy and not cool,” he said. “So we insisted on the supernatural, ghost story, gothic horror aspect, which is consistent with many tales of the sea. Once you buy into sword-fighting skeletons, the eye patch, buried treasure and monkeys are not such a big deal. These pirate films are really ghost stories set in a world of pirates.”