On this day 87 years ago, Japanese troops slaughtered up to 300,000 Chinese in a horrific massacre that made even the Nazis tremble. “To forget a Holocaust is to kill twice,” and the “forgotten Holocaust of WWII” truly has been forgotten.

Over a period of six weeks, the Japanese terrorized the Chinese city of Nanjing in what is known as the Nanjing Massacre or the “Rape of Nanjing.” In addition to the mass murder, Japanese troops also committed other war crimes such as mass rape, looting, and arson. Up to 80,000 women were raped, and around a third of the buildings in what was then China’s capital were destroyed. Read on to learn more about this largely forgotten chapter of WW2.