The Flash, Green Arrow, Supergirl, Firestorm and almost every other superhero in the Arrowverse teamed-up last week to fight nazi versions of themselves, and the results were as impressive as any cinematic experience.

RELATED: Crisis on Earth-X's Most Bad-Ass Moments

The Crisis on Earth-X event took over The CW's entire superhero line-up, unfolding over two nights and spanning nearly four hours. With the cast of Supergirl, The Flash, Arrow and Legends of Tomorrow all on deck, the producers and filming crews had their work more than cut out for them. A new behind-the-scenes video looking at The Flash's respective hour of the crossover event was just released, giving us a look at just how massive the production actually was.

The video dives into the superheroes' attack on the nazi compound as they attempted to return to their Earth, and it gives us insight as to how the crossover event managed to pull-off movie-worthy stunts and action scenes on a television budget. "It was massive," says Curtis Braconnier, the fight coordinator for the sequence. "I think as a performer and a coordinator it has been the biggest three days of my whole career," he says of the sequence that involved 22 performers, from actors to stunt doubles, and explosions, wirework and fight choreography. "It was absolute madness."

RELATED: How Crisis on Earth-X Became the Arrowverse's Best Crossover Yet

This year’s four-part crossover “Crisis on Earth-X” aired across two nights, on Supergirl and Arrow (on a special night for one week only), The Flash and Legends of Tomorrow.