The Nanjing massacre was an orgy of violence in which Japanese soldiers murdered tens of thousands of Chinese soldiers and civilians.
Although it took place more than 70 years ago, it is still remembered with anger in China, and continues to taint the country's relationship with Japan.
Chinese director Lu Chuan hopes his new film about the incident, called City of Life and Death, will help heal some of those wounds.
But the making of the film, and the subsequent public reaction, has revealed just how difficult it will be for the movie to achieve that goal.
While it was being filmed, there were disagreements between the Chinese and Japanese actors - and a fight.
And since its release the director has received a death threat and a storm of unfavourable comments from angry Chinese film-goers.
The movie, filmed completely in black and white, is already being seen as a box-office success, despite not opening until the end of last month.
It took 120 million yuan ($17.6m, £11.7m) in its first 10 days and has been showing in more than 500 cinemas across the country.
It is a bleak film, with scenes of rape, murder and cruelty.
In an interview with the BBC, the director said he had wanted to make a movie that represented the truth of what went on in Nanjing.
"The relationship between China and Japan is very unstable. There is too much misunderstanding between each other," he said.
The 38-year-old said he wanted to show the movie in Japan to let ordinary people there know why so many Chinese people still hate them.
According to the director, and many of his compatriots, the Japanese have not yet properly apologised for their wartime aggression - including the Rape of Nanjing.
But the director, from Beijing, said there was also a message for Chinese audiences.
"It's very important to tell Chinese people that Japanese people are human beings - not beasts," he said.
To show both sides of the story, the film contains a sympathetic portrayal of a Japanese solider, who eventually commits suicide.
Many of those who have seen the film have applauded this angle.
"It's different to other films about the Nanjing Massacre. It tries to look at the war through Japanese eyes," said 32-year-old student Zhu Xiaojie, just after watching the film.
But there are many Chinese film-goers who do not want to confront the fact that some Japanese soldiers might have felt disgust for what they did.
There have been thousands of internet postings about the film - some by people who believe Mr Lu has done China a great disservice.
"It's not a movie for patriotic education, but a Japanese movie shot by a Chinese director," read one posting.
After seeing the movie, other Chinese people said they would not buy or use Japanese products ever again. One went even further.
"I received a letter without a name on it that said someone wanted to kill me, eliminate me," said the softly spoken Mr Lu.
The director said he was not afraid, but he admitted that he had changed his routine when going out in public places.
And there was the on-set fight between Japanese and Chinese actors.
Mr Lu said the altercation happened while they were shooting a scene showing Japanese soldiers dancing to the beat of a giant drum.
To shoot the scene, two drummers were flown in from Tokyo, but got into an argument with a group of Chinese actors.
One drummer, angry at the noise around him while he tried to concentrate, hit a Chinese actor, according to the director. The argument then escalated.
"My assistant ran to me and told me that something very bad had happened. I was so surprised," said Mr Lu.
Relations between China and Japan have improved over the last couple of years.
Japanese Prime Minister Taro Aso visited Beijing just last week and had only good things to say about the current relationship.
The two countries agreed to work together on a range of issues, such as getting North Korea to give up its nuclear programmes.
But the experience of the film shows that there is still deep mistrust - mistrust that Mr Lu's film will not completely eradicate.