The time has come for History Channel’s “Vikings” to launch their attack on Paris, and in the April 9 episode, we see Ragnar (Travis Fimmel) and his horde of northmen assailing the supposedly impenetrable walls of the city.

Below, Variety has an exclusive sneak peek at the Vikings’ assault on Paris, and we talked to creator Michael Hirst about the process of recreating the city for season three of the ambitious series.

As with everything on “Vikings,” historical accuracy was key for Hirst: “The Vikings actually attacked with a hundred ships and 3,000 men, so it’s not only Ragnar who had to get ready and step up, so did the production,” he told Variety . “It was like the show mirroring actual Viking experience, because we know that the Vikings started off with one or two ships going west and attacking lonely monasteries with 30 warriors or something like that. And then, before very long, there were lots more raiding parties, much more ambitious raiding parties, and finally the attack on Paris with a huge number of Viking warriors.”

The change in scenery also allowed the show to create more lavish sets, with a European city providing a vastly different backdrop than the landscapes the series has explored thus far. “It was great for the production to go to a different world, so we built the inside of Notre Dame Cathedral on one of the stages,” Hirst said. “It’s one of the biggest stages in the world and it was the biggest build that we’ve done so far, and it’s amazing. Marble floors, stained glass windows, hundreds of statues… Then we built part of the walls of Paris on the backlot. We built the bridge leading into Paris on the backlot. We had to have more boats and more stunt people and more extras, so when you went around there it was like an army. Suddenly there were thousands of people around. There were hundreds before, now there are thousands.”

Hirst credits stuntmen Franklin Henson and Richard Ryan with perfecting the complex fight scenes for the attack on Paris. “We’re lucky. We have two of the greatest guys who do our choreography for the fight sequences, and they were in their element. They actually trained up a lot of Irish people, men and women, to be stunt people. We needed so many stunt people. I always like the fact we employee so many Irish people, and it knits everything together. But the choreography was extraordinary and very, very dangerous. One of the things I love about ‘Vikings’ — it’s real. Our guys really do fight and they climb and they ride and they row and they love it, but this was at a different level because we’re setting fire to the ladders. We have people falling 50 feet into water, and watching that is heart-stopping.”

“Vikings” airs Thursdays at 10 p.m. on History.