In a grotty hutong, tucked behind the neon signs of Ghost Street and the bustle of the Lama Temple, is a gray tower. The turret is trimmed with rusted barbed wire covered with vines and weeds, a green leafy crown on a forgotten centurion. The tower is one of four remaining guard posts for the Pao Ju prison, known in Beijing slang as Lao Pao’er, a notorious detention center which housed some of China’s most famous traitors, spies, and criminals.

It is also part of the Beijing lexicon. An old Beijing saying warned miscreants of their fate: “If you’re not good and honest, you’ll be sent to the Pao’er.” Many Beijing hoodlums, big and small, did time at Pao’er. Some did more than one stint. Alumni of the prison, especially repeat offenders, earned the nickname “Lao Pao’er,” which entered Beijing slang as another word for criminal or somebody who was an overall badass comfortable with stretching the bounds of legality in their day-to-day life.