In classic mythology, below Uranus (sky), Gaia (earth), and Pontus (sea) is Tartarus, or Tartaros (Greek: Τάρταρος, from τάρταρον "tartar encrusting the sides of casks"). It is a deep, gloomy place, a pit, or an abyss used as a dungeon of torment and suffering that resides beneath the underworld. In the Gorgias, Plato (c. 400 BC) wrote that souls were judged after death and those who received punishment were sent to Tartarus.
Like other primal entities (such as the earth and time), Tartarus is also a primordial force or deity.
Tartarus was used as a prison for the worst of villains, including Cronus and the other Titans who were thrown in by Zeus. Uranus also threw his own children into Tartarus because he feared they might overthrow him. These mishaps included the "hundred-handed-ones", the "cyclops" and the "giants".