The advances in visual effects in television has made it difficult to tell what’s real and what isn’t, especially on a program like Vikings. That’s where the folks at Mr. X and Take 5 come in. The production houses are charged with creating everything in History’s Thursday night drama, from Ragnar Lothbrok’s longboats to King Ecbert’s expansive compound to the soaring peaks surrounding Kattegat.

That work falls to Mr. X Inc. and Take 5 Productions, two studios specializing in visual effects and animation for television and feature film.

“We get scripts later in the process than the producers and the directors,” Dominic Remane, visual effects supervisor at Mr. X, says. “We’ll make a note of an establishing shot of Kattegat that has to start high and wide, or a fleet of 60 longboats leaving Kattegat for Wessex.” From directions in the script, Remane and his team of 60 know they’ll have to add in more of Ragnar’s ominous ships—only a handful of real longboats exist—and that the end of the real lake the boats are on needs to be deleted and elongated to look like a Scandinavian fjord.

Bill Halliday, visual effects producer at Take 5, says both companies see Vikings as a project with the hallmarks of a feature film look hemmed in by the constraints of a television show budget. And, as Halliday points out, Vikings regularly surpasses movies when it comes to the number of visual effects done in one episode.

“In the first episode of Season 3 there were over 100 visual effects, which by television standards is a huge amount,” Halliday explains. “In Episode 8, the invasion of Paris, there are over 300 visual effects which is remarkable. I worked on The Tudors and we did fewer effects in a season than we would on one episode of Vikings. A feature film runs around 200 visual effects.” It’s a stunning scope, Halliday explains, and one that—if everyone has done their jobs right—nobody notices.

A difficult aspect of the job with regard to Vikings is meeting the demand of show creator Michael Hirst, whose imagination pushes everyone to be creative. There have been times when they couldn’t deliver; Halliday notes a recent request to create a fully-digital animal to interact with a character couldn’t be created within the short time frame TV works in.

Perhaps the biggest jewel of Vikings’ Season 3 crown will be Ragnar’s invasion of Paris. It’s a story angle that’s been ramping up all season and cast member Clive Standen told me it will blow viewers’ minds. Remane worked closely with the show’s production designer, Mark Geraghty, to research the oldest castles in Europe to base Ragnar’s 850 AD attack on. They found it in Carcassonne, France, where surveying was done to select parts for which they could base Paris of the time period on.

“I’ve always wanted to be working in visual effects, but I never thought I’d be doing it to this level,” Remane admits. “I never thought I’d be going to Europe, France and Ireland, going to Norway and filming plates for the show.”

Vikings airs Thursdays at 10 p.m. ET/PT on History.