The religion of Greek mythology has no physical text like the Bible in Catholicism or the Quran in Muslim. Instead similar to the beginning of our Catholic religion the stories, myths and legends were passed on orally. Some stories were used to write poems which became great literature. The poet Homer's 8th-century BC epics the Iliad and the Odyssey, for example, tell the story of the (mythical) Trojan War as a divine conflict as well as a human one. Greek mythology centers on Gods (goddesses), heroes, monsters and theology (cosmogony). We font know when Greek mythology actually started because it's a collection of stories never written down, but we do know the oldest story is about the Trojan War. Greek mythology covers everything from the creation of "races" to how Gods achieved there god-hood.it also covers some things the bible cant or doesn't explain there are stories in Greek mythology stating how all the races we have today were created and there story, Greek mythology is obviously polytheistic as in they believe in many gods, while Christians are monotheistic and only believe in one god. Greek mythology has one god Zeus who is the highest of all the gods but he has many sons, daughters, brothers, sisters and wife's who make up the rest of the deities.
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Theology.
The creation of the world is similar to the creation story in the bible, in which a shapeless nothingness was made into earth however in Mythology they believe that in arises from chaos. And Gaea (earth), the ever-sure foundation of the immortals created the earth with others Gaea put Uranus (sky) over her, from chaos came Erebus (darkness) and Nyx (night), of Nyx was born Aether (brightness) and Hemer (day), Hypnos (sleep) and Thanotos (death) who are brothers. This story goes on until we are brought to a new breed of god, a titian Cronus, three gods and three goddesses, the Cronus who will be joined with the children of Zeus to comprise the twelve Olympians.