The truce did allow those religious pilgrims who were travelling to Olympia to pass through warring territories unmolested because they were protected by Zeus.[8] The origin of the Olympics is shrouded in mystery and legend;[9] one of the most popular myths identifies Heracles and his father Zeus as the progenitors of the Games.[10][11][12] According to legend, it was Heracles who first called the Games "Olympic" and established the custom of holding them every four years.[13] The myth continues that after Heracles completed his twelve labours, he built the Olympic Stadium as an honour to Zeus. Following its completion, he walked in a straight line for 200 steps and called this distance a "stadion" (Greek: στάδιον, Latin: stadium, "stage"), which later became a unit of distance.