For actor Tom Cullen, preparing for the leading role in History's legendary new series Knightfall was "a trial by fire".In the show, Cullen stars as Landry, an elite Templar Knight on a quest to rediscover the Holy Grail. Considered the "most advanced special forces" of their time, according to Knightfall stunt coordinator Cédric Proust, these armored warriors were the medieval equivalent of the U.S. Navy's SEAL Team Six.So it should come as no surprise that Cullen's training program leading up to filming was a crash course in sword training, grueling workouts, and a protein-rich diet of lean meats.But while building a bulked-up physique was essential to looking the part, learning how to wield a sword medieval-style was critical to shooting the series' large-scale battle scenes. Cullen hadn't picked up a sword since drama school, but he was more than game to get back on the horse."Tommy's quite an athletic guy" and "he picked [the battle choreography] up quickly," says Proust.That doesn't mean he didn't have to work his ass off to get there."I had three months to get myself into a physical condition, whereby I looked like someone who'd been fighting in a war since he was 11 years old," Cullen explains. He endured a two-week boot camp, boxing, circuit training, sword fighting, practicing battle choreography, and horse riding. "I've always been fit," he adds, "but to get big and strong like that was a real fun journey and challenge to go on."The Knightfall season finale airs on Wednesday, February 7 at 10 p.m. on History.