Detention as a form of punishment dates back to Roman times and beyond. The historical image of the dark, dingy dungeon was supposed to have been replaced by modern ideas of reform and rehabilitation in the 19th century.
However, in many societies today, poor prison conditions, mass incarceration, and the resulting issue of overcrowding have once again become a focal point for human rights and social justice protests.
Many prisons are costly to run, often understaffed, and can have a dangerous impact on the environment. Those who are incarcerated can experience grim conditions, with inadequate access to healthcare, experience deterioration of their mental health, and may face violence and abuse from other prisoners or staff.
While the violence of the American prison system is well-known, overcrowding, inhumane conditions, and punitive political attitudes driven by the fear of crime are increasingly critical prison issues worldwide.
Many of the world's largest prisons – listed by population – are filled to over capacity, with the Institute for Crime and Justice Policy Research estimating that there are 11.5 million people in prison across the world.
Globally 140 people per 100,000 are in prison on any given day.
Here is our list of several of the largest prisons in the world.