Erebos (place)

Erebos, also spelled Erebus (Ancient Greek: Ἔρεβος), is the name for the great black walls of Hades' Kingdom. He is also the son of Chaos, brother to Gaea, Tartarus, and Nyx, as well as a consort. He represented darkness which filled the nooks and crannies of the world. He is often exchanged with Hades and Tartarus since Erebus is often thought as part of the Underworld.

History
Erebus is the god of Darkness and Mist, one of the original primordial gods, a child of Chaos. His wife and sister was Nyx. He was the father of many beings, and also the name for the desolate plains of the Underworld, as well as the walls where he currently resides. With Nyx he is the father of Hemera, the Primordial goddess of the day, and Aether, Primordial god of Light, an ironic fact that the day and light would be the children of night and dark. His other children include: Momus, Nemesis, Hypnos and Thanatos.

Some accounts say that Hades is completely dark because of him. It's said that once Erebus was conspiring against the gods and planing to enter Tartarus and bring back the Titans. Nevertheless, Hades found out and surprised the conspirators, throwing Erebus in Tartarus and locking him there. According to that myth, since that day, Hades became only brighter than Tartarus. This version is strange because Erebus is a primordial god and wouldn't likely be defeated by any of the Olympian gods, even if surprised.

The Lightning Thief
Though the actual being is not seen in the series, Percy sees the part of the Underworld called Erebos while he was on Charon's barge when he goes to the Underworld for the first time.

The Last Olympian
Percy sees the place Erebos in the distance as he makes his way towards the the River Styx after escaping from Hades' Palace.

Description
Erebus is the protogenos of Darkness and Mist, one of the original primordial gods a child of Chaos, his wife and sister was Nyx. He was the father of many beings, and also the name for the desolate plains of the Underworld, as well as the walls where he currently resides.

In some stories, Erebus is a region of the Underworld where the dead had to pass immediately after dying, he is sometimes used interchangeably with Tartarus. Erebus was never actually named in the series.