Introduction to mass grave sites: "Mass graves" were created after the Japanese invaders occupied the Datong Coal Mine in October 1937 and brutally implemented the bloody policy of "exchanging people for coal". The tunnel of corpses. The Japanese invaders occupied the Datong Coal Mine for eight years, plundering more than 14 million tons of coal, and more than 60,000 miners were tortured to death. There are more than 20 "mass graves" in the Datong coal mine area alone, and only two remain. This is irrefutable evidence of the Japanese army’s murder of Chinese miners and of Japan’s crime of invading China. Now the "mass grave" site of Datong Coal Mine has been used as a base for national defense and patriotism education, always reminding people not to forget the national humiliation.