[This story contains spoilers for the first two episodes of Percy Jackson and the Olympians season two.]

The first season of Percy Jackson and the Olympians had a fair number of action sequences, including Percy (Walker Scobell) fighting the Minotaur in the series premiere, Camp Half-Blood’s capture the flag game and Percy’s climactic fight with Ares (Adam Copeland). Nothing, however, was to the scale of what the show pulled off in season two’s second episode.

The show pulled off its biggest action sequence so far by staging a chariot race — on a track built for the occasion, with real horses instead of VFX creations — to determine which demigod would lead a quest for the Golden Fleece. The huge physical set and complicated filming process are part of an overall effort to make season two, based on Rick Riordan’s novel The Sea of Monsters, feel bigger and more immersive.

“I’ve always been a huge fan of a built environment. I love going to a real location,” director and executive producer James Bobin, who helmed the first two episodes of season two, told The Hollywood Reporter. For the chariot race, he added, “We built what I call the circus minimus, a small version the Circus Maximus. We used these incredible statues that [production designer] Dan Hannah built for us. And the track is literally a quarter mile long. It’s a huge thing.“

The track and surrounding grandstands rose out of a field in British Columbia near the show’s Camp Half-Blood set. Bobin said he and Hannah had lengthy discussions about making the arena feel impressive for the size of the camp, but not so huge that it would make the few hundred background actors playing campers look lost. Hannah and his team also built chariots specific to each Camp Half-Blood cabin, with a trident adorning Percy and Tyson’s (Daniel Diemer) for the Poseidon cabin and a steampunk version for the Hephaestus cabin, among others.

The race plays a key part in kicking off the primary story in The Sea of Monsters (and the show): After Luke (Charlie Bushnell) poisons Thalia’s tree, which generates the protective barrier around the camp, campers need to find the Golden Fleece and use its healing powers to repair the tree before the barrier falls completely and Luke and his forces, who are loyal to the Titan Kronos, overrun it.

Percy thinks he and Tyson can team up with Annabeth Chase (Leah Sava Jeffries) so that one of them wins the race and thereby leads the quest. Annabeth, however, has been told by the camp’s ousted activities director, Chiron (Glynn Turman), that due to a prophecy, Percy needs to be kept — at all costs — from joining her, so she reluctantly agrees not to help him.

When it came time to film, the show had 30 live horses brought in. Bobin said the show’s creative team made an early decision not to add the horses via VFX (though there are still a large number of effects shots in the completed sequence). “I love the idea of the sweat of the horses, they’re running and the flared nostrils and all that. I’m a huge fan of that original Ben-Hur style of shooting, whereby you feel the heat and the weight of the horses and hooves on the ground,” Bobin said. “I was very keen to get involved with that. We had a fantastic horse trainer. Our stunt guy, who sadly passed, Danny [Virtue], was just amazing, and he did a fantastic job.” The episode is dedicated to Virtue, a long-time stunt coordinator and performer and animal coordinator who died in September.

The actors were psyched to perform on the track as well. “Actually getting to ride the chariots and fight on them — it’s weird,” Scobell told THR. “In my mind, when I’m talking to people about it, I don’t think of it as like, ‘oh, I was pretending to do it.’ I feel like I did. The chariots were awesome. The armor was so cool. It’s one of those things that just feels so awesome to do it. I don’t know how else to explain it.”

There was one problem, though: Safety regulations state that a live horse and an actor who’s a minor — as Scobell, Jeffries and several other members of the cast are — can’t be in the same shot. Bobin and his team worked around it, using trailers and stunt performers and editing in such a way to satisfy the regulations while still providing the visceral feeling he wanted to capture.

Diemer, who plays Tyson, a Cyclops and Percy’s half-brother, said getting to be in motion around the track made playing the scene more real — and more fun. “Aesthetically, it’s just gorgeous, it really is. Outside of that, whenever we’re not working directly with the horses for safety reasons, we’re still working with sets that are moving. We have trucks that are pulling things along, we’re doing stunts on the chariots, we’re actually fighting in these spaces. You get the whole experience of actually maneuvering through the set, through the action. There are no places where we’re just standing still, pretending that things are moving. I think the audience is going to feel it along with us.”

With Percy and Annabeth working at cross purposes — and an attack by a flock of Stymphalian birds that the two then fend off — neither ends up winning the race. Instead, Clarisse La Rue (Dior Goodjohn), a daughter of Ares and Percy’s season one nemesis, takes the prize and gets to lead the quest.

“She gets to camp [in season two] and she’s trying to redeem herself with these chariot races and prove herself to Percy. But Percy comes back and he’s six feet taller” — Scobell had a noticeable growth spurt in the long gap between filming seasons one and two — “and we’re like, well, that wasn’t in my bingo card. So she’s starting off at a rough place, then she gets the opportunity to redeem herself — not just at camp, but also with Olympus. She has a chance to redeem herself and her family.”

“It’s more about the story of the set piece and the set piece itself,” said Bobin. “The story was about Percy being betrayed by Annabeth and Clarisse winning. It’s the stories you have to tell, as well as making it work at all, which is one of the great miracles of film. That was what my job was, to make sure those pieces work together, and at the same time we’re telling a story whereby you appreciate Clarisse, because she is who she is and never gives up and goes on to win. Percy has to give up because he’s trying to save his friend. It was a great joy to film. It was hard work, but we’re so pleased with the outcome.”