“My job is creating worlds,” says production designer Gemma Jackson, who did just that on the first three seasons of HBO’s “Game of Thrones.”

Her task now: inventing the world of King Arthur, the legendary British monarch of medieval times, for helmer Guy Ritchie’s latest movie, which starts filming next February for a 2016 release.

“It’s an original take on the King Arthur myth,” says Jackson. “But it’s Guy, so it’s not a traditional period film. It has to have a modern edge to it.”

Pre-production on “King Arthur” began in March. “We spent three months coming up with concepts, which were presented to Warner Bros.,” Jackson says. Since very few visual records exist from the 6th century, “we had to delve into our imaginations,” Jackson says. “It’s a very original take on the story.”

The Warner Bros. picture will shoot at the studio’s own Leavesden Studios outside of London, where the Harry Potter films were also shot.

And, like those movies, it’s a big film, Jackson notes. “Every day is already full to bursting, and I’ve got a whole roomful of people working away out there.”