Greek mythology is the body of myths that belong to the ancient Greeks and deal with the numerous Greek gods and heroes of ancient times. It was a part of the religion in ancient Greece. Greek mythology is known today primarily from Greek literature and representations on visual media dating from the Geometric period from c. 900-800 BC onward. In fact, literary and archaeological sources integrate, sometimes mutually supportive and sometimes in conflict; however, in many cases, the existence of this corpus of data is a strong indication that many elements of Greek mythology have strong factual and historical roots.
Greek mythology has changed over time to accommodate the evolution of their culture, of which mythology, both overtly and in its unspoken assumptions, is an index of the changes. The earlier inhabitants of the Balkan Peninsula were an agricultural people who, using Animism, assigned a spirit to every aspect of nature. Eventually, these vague spirits assumed human forms and entered the local mythology as gods. When tribes from the north of the Balkan Peninsula invaded, they brought with them a new pantheon of gods, based on conquest, force, prowess in battle, and violent heroism. Other older gods of the agricultural world fused with those of the more powerful invaders or else faded into insignificance.
The achievement of epic poetry was to create story-cycles and, as a result, to develop a new sense of mythological chronology. Thus Greek mythology unfolds as a phase in the development of the world and of humans. While self-contradictions in these stories make an absolute timeline impossible, an approximate chronology may be discerned. The resulting mythological “history of the world” may be divided into three broader periods: