A Greek legend tells of the great Heracles (or Hercules, in Latin) who won a race at Olympia and then decreed that the race should be re-enacted every four years. Another legend says that Zeus had instated the festival after his defeat of Cronus. According to yet another legend, King Iphitos of Elidos consulted the Pythia (oracle of Delphi) to try and save his people from war in the 9th century BC. The prophetess advised him to organize games in honor of the gods. The Spartan adversary of Ipitos then decided to stop the war during these games, which were called Olympic, after the Olympus, the mountain on which the Greek gods were said to live.

The Olympic Games were held in Olympia, a worshipping place for the Greek gods where an ivory and gold statue of Zeus was kept. The first written accounts of the Olympic Games date from 776 BC, although it is certain that these Games were not the first ones to be held. The only competition held then was the stadion race, of about 190 meters, measured after the feet of Hercules. (The English word "stadium" is derived from this foot-race.) The Olympic Games were held with four year intervals, and later the term "Olympiad" for the period between two Games was adopted.

Over the years, the festival grew from one to five days, of which three were used for competition.