The Olympic Games were a series of athletic competitions among representatives of city-states of Ancient Greece. They were held in honor of Zeus, and the Greeks gave them a mythological origin. Historical records indicate that they began in 776 BC in Olympia. They continued to be celebrated when Greece came under Roman rule, until the emperor Theodosius I suppressed them in 394 AD as part of the campaign to impose Christianity as the state religion of Rome. The games were usually held every four years, or olympiad, which became a unit of time in historical chronologies.