Introduction to the lower cave of the mass grave: The "mass grave" is located in the south ditch of Meiyukou in the mining area of Datong City, and is divided into two caves: the upper cave and the lower cave. The upper cave is more than 5 meters wide and 40 meters deep. It is a natural cave. The lower hole is about 4 meters wide and more than 70 meters deep. It is the tunnel of an old small coal kiln. The two caves are filled with corpses of miners who were killed or tortured to death after the Japanese occupied Datong during World War II. According to historical records in the collection, the Japanese invaders occupied Datong for eight years. In the name of building houses and roads, they lured or forcibly captured a large number of farmers and handicraftsmen in Beijing, Tianjin, Shandong, Henan, Jiangsu, Hebei, Anhui and other places to work as miners in the mines. They implemented a barbaric policy of "exchanging people for coal" and threw more than 60,000 miners who were tortured, killed or dying of illness into caves and old coal mines. Over time, they formed "mass graves" filled with bones. The pit entrance in Nangou, Meiyukou, is only one of more than 20 "mass graves" in the mining area.