A peaceful rally turns deadly in "Peterloo" (Simon Mein/Amazon Studios)

“Peterloo” is a big, big movie. Which means it’s odd Mike Leigh directed it, since his films — which include “Secrets & Lies” and “Vera Drake” — are usually small, quiet and intimate. Though Mike Leigh doesn’t find it odd.

“People have said to me, ‘You’ve never done a battle scene before,’ ” he says. “That’s not true. You’ve seen my battle scenes, but usually it’s a battle between two or three people on the staircase of a suburban house, or arguing in a kitchen. But a battle is a battle.”

The battle at the center of this 152-minute film is really a massacre. On Aug. 16, 1819, tens of thousands of people gathered at St. Peter’s Field in Manchester, England. They were rallying for political reform; among other demands was the right for every adult male — not just landowners — to have the right to vote. During the peaceful demonstration, members of the military on horseback charged into the crowd, swords drawn. In the ensuing chaos, at least 10 people were killed and hundreds injured. The incident was named the Peterloo Massacre as a nod to the bloody Battle of Waterloo four years before. (“Peterloo” is an Amazon Studios production; Amazon chief executive Jeff Bezos owns Express.)

Leigh’s film builds slowly to the nearly final scene depicting the massacre. In that scene, it seems that chaos reigns.

“The main thing was to have it very well planned and organized, but not for it to lose its organic spontaneity,” Leigh says. The scene took five weeks to shoot, and, “The actual shooting, when it all spins out of control, obviously took a lot of planning. Having said all that, when we first did the bit where the [soldiers] come in and start slashing with their swords, it was terrifying. The actors … were kind of traumatized it, because it seemed real.”

Leigh is perhaps best known for rehearsing with his actors for close to six months before heading off to the shooting location. “Peterloo” has a huge cast, as Leigh tracks multiple groups of characters, including a family whose son returned from the Napoleonic Wars with a pretty clear case of PTSD, as well as the political reformers and those who gave the order to charge. But he still felt it was important to keep the tradition going. His rehearsal process, he says, enables the actors to find fully realized characters.

“It’s about making the characters alive. My philosophy, irrespective of the film, is to put on screen people you can believe in as being real, not ciphers,” he says. “When I was a kid, I’d go to the movies as often as they’d let me. I’d sit in the cinema and think, ‘Wouldn’t it be great if you could have a film where the characters were like real people?’ In the 1940s and ’50s, people in films weren’t like you and me. So that’s always been my sort of thing.”