More than 10 Chinese managed to escape from the prison, but most died soon after being recaptured or from hunger and injury. Only a few managed to survive.

One of the survivors-who died on the battlefield fighting the Japanese two years later-was the inspiration for the film's plot. Quan conceived the script as a tribute to mark those lesser-known heroes.

China's revolutionary titles are mostly produced by Chinese mainland companies, but Cliff Walkers attracted the attention of the Hong Kong studio Emperor Motion Pictures, which is one of its main producers and will handle the movie's international distribution.

Alex Yeung, vice-chairman of Emperor Motion Pictures and the movie's co-executive producer, recalls that his father Albert Yeung met with director Zhang for the first time in June 2018.

"They hit it off immediately. They soon agreed to collaborate on a quality film that makes people shout 'bravo'. In the same year, we further developed this film and production kicked off in 2019," recalls Alex Yeung.

Datong in Shanxi province doubles as old-time Harbin, with reconstructions of buildings and streets, while snowy scenes were shot in Xuexiang, or Snow Town, in Heilongjiang province.

Admitting that the film has also enriched his knowledge about China's revolutionary martyrs, he says: "I felt quite overwhelmed when I heard this story for the first time. That generation (the early members of the Communist Party of China) was stoic and dedicated. They are the true nameless heroes who contributed to build a safe and harmonious society and deserve to be remembered."