The ancient Greeks believed every person, man, woman, or child, that lived on earth went to Hell or Hades upon death. Every single person. They also believed that if your existence was so painful that you could drink deeply from the river in the underworld and you would be reincarnated.
Doing this, however, offered no guarantees that your new existence would be less painful than your previous one though and in the end, you ended up back in the same place you started. Hell.
The river was called Styx.