religion had two main sources and levels, and although there have been many attempts by poets and philosophers alike to make these two levels coherent and harmonic, they never quite managed to do it. These two levels are: The Chthonic Deities
and tradition and the Olympic Deities
The basis of most of what we know of the myths surrounding the Chthonic Deities comes from the two surviving poems of Hesiod: Theogony and Works and Days (or in Greek 'Erga kai Hemerai'), whereas the Olympic tradition derives mainly from Homer.
The Chthonic tradition is much earlier than the Olympic one, and thus is more wild, mystic and 'uncivilized' than it.
Chthon means earth or soil in Greek, and indeed they were believed to dwell in the earth or beneath it. Most of these deities were connected with the basic, yet crucially important and threatening things in life: fertility, death, the dead, illnesses, magic etc. and most were believed to be active mainly in the night. Thus religious worshipping of these deities were conducted in the night, and sacrifices were made by pouring liquids onto the earth, by throwing beasts into pits, or by burying them. All the daimones are Chthonic Deities.
Some Chtonic Deities later were viewed as Olympic Deities as they became more important to the Greeks, but they never lost their characteristics as Chthonic Deities, no matter how much the Greeks tried to hide them. Such deities are: Hades, Demeter and Dionysos.
Greek and Roman Mythology