The Games took place in a four-year cycle known as the Olympiad, which was one of the ways the Greeks measured time. The Olympic Games were used as a starting point, year one of the cycle; the Nemean and Isthmian Games were both held (in different months) in year two, followed by the Pythian Games in year three, and then the Nemean and Isthmian Games again in year four. The cycle then repeated itself with the Olympic Games. They were structured this way so that individual athletes could participate in all of the games.
Participants could come from all over the Greek world, including the various Greek colonies from Asia Minor to Spain. However, participants probably had to be fairly wealthy in order to pay for training, transportation, lodging, and other expenses. Neither women nor non-Greeks were allowed to participate, except for very occasional exceptions such as Philip II of Macedon or Nero.
The written history of the Olympic Games dates to 776 BC, but their actual founding was centuries earlier. The other three games were founded in the 6th century BC.
