More than a year before "The Blair Witch Project" hit theaters and became a cultural phenomenon, its central mystery had already gone viral.

According to the movie's fledgling promotional website, which presented itself as a real investigative project, three film students — Heather, Mike and Josh — had ventured into the Maryland woods in 1994 to shoot a documentary and then disappeared. Their footage was recovered a year later, providing evidence to support a disturbing legend. The online message boards began to buzz, with questions about the story's veracity.

The hype, intrigue and skepticism surrounding the account, fueled by the internet's advent, grew through the movie's premiere, in July 1999. What eventually emerged — a feature-length film made of spliced together scenes of shaky home video footage — made the demise of its three characters seem all the more authentic and terrifying.

Of course, the whole thing was fiction. But a lot of viewers didn't know that going in.

"The prime directive we had was that the film had to look completely real," said Eduardo Sánchez, who, along with Daniel Myrick, conceived and directed the entire thing, from the manufactured legend to the film itself.

"The lighting had to make sense, the sound couldn't be great," he continued. "There wasn't going to be a soundtrack. It was just edited footage."

Released 20 years ago, "Blair Witch" remains an inflection point for the movie industry. Produced for $60,000, the film made $248.6 million at the global box office. Its amateur aesthetic prompted a generation of filmmakers to pick up a camera, however low-tech. It exposed new possibilities for marketing in the internet age. And it was a ubiquitous part of pop culture, spawning myriad imitators and spoofs, in turns inspired by and mocking its shaky cinematography and selfie-style confessionals.

"Blair Witch" could also be just plain scary — in a way that tapped perfectly into the trends and anxieties of the moment.

"In many ways mainstream moviegoing audiences simply forgot horror could be scary in this way," said Alexandra Heller-Nicholas, author of the book "Found Footage Horror." "There was something in the air in 1999 that made us acutely aware that technology could be linked to some kind of vague, chaotic unknown, and 'Blair Witch' tapped into this at exactly the right moment."

It didn't invent the found-footage movie. Film historians credit Ruggero Deodato's 1980 thriller "Cannibal Holocaust," which similarly featured the disappearance of a young movie crew, as the first. But the "Blair Witch" creators understood there was a fresh appetite for the concept. By 1999, reality TV programs like "Cops" and "The Real World" were on the rise, and the internet was providing a conspiratorial and conversational hub for its users.

That convergence primed viewers for a low-fi aesthetic that, in the right hands and with the right idea, could lead to something novel. It also allowed for an extremely low budget.

"For us, video was about to become as good as film," Sánchez said. "All of a sudden, you could edit on your computer." Audiences seemed willing, he added, to accept "these new types of media and new types of stories that were being told."

Myrick and Sánchez's surprising success inspired many young filmmakers to view amateur equipment as an opportunity, not a limitation.

"Everyone now can afford a camera — has a camera in their pocket — and can, if they think out of the box properly, do something very new," said Aneesh Chaganty, director of the breakout thriller "Searching," from last summer.

He added: "Seeing a group of people like the whole team behind 'Blair Witch' succeed at the level they did back then was an injection of adrenaline as filmmakers."

Would the filmmakers' tactics still be successful today? Even they admit that it would be unlikely.

"Now it wouldn't work," Sánchez said. One could easily look find out on the internet that Heather from "Blair Witch" was an actress named Heather Donahue — who hadn't disappeared at all.

Nonetheless, the deeper lessons about connecting with fans in a media-driven age are still relevant.

"I think 'The Blair Witch Project' was the first example of what the power of fandom would do in Hollywood," said Mike Monello, a producer on "Blair Witch" who went on to launch Campfire, an entertainment-marketing agency. "When you connect fans together on the internet, their shared passion deepens."

As with a lot of other things, timing is everything, he said.

"We understood what we were doing on some level," Monello said. "But an awful lot of it was right place, right time, right story. It all converged."