The Greeks were polytheistic in their religious beliefs. Polytheistic means they believed in and worshiped many different gods. In Greek mythology, the gods often represented different forms of nature. Their religion/mythology had no formal structure with the exception of various festivals held in honor of the gods. There was no sacred book or code of conduct to live by. The most powerful Greek gods were known as the Olympians. The Greeks believed the Olympians lived on the highest mountain in Greece, Mount Olympus. The Olympian gods included: Zeus, Hera, Apollo, Aphrodite, Ares, Artemis, Athena, Demeter, Hades, Hermes, Hephaestus, Poseidon and Hestia or later she was replaced in some lists by Dionysus.