Only free men who spoke Greek were allowed to participate in the Ancient Games of classical times. They were to some extent "international", in the sense that they included athletes from the various Greek city-states. Additionally, participants eventually came from Greek colonies as well, extending the range of the games to far shores of the Mediterranean and of the Black Sea. To be in the games, the athletes had to qualify and have their names written in the lists. It seems that only young people were allowed to participate, as the Greek writer Plutarch relates that one young man was rejected for seeming overmature, and only after his lover, who presumably vouched for his youth, interceded with the King of Sparta, was he permitted to participate. Before being able to participate, every participant had to take an oath in front of the statue of Zeus, saying that he had been in training for ten months. At first, the Olympic Games lasted only one day, but eventually grew to five days. The Olympic Games originally contained one event: the stadion (or "stade") race, a short sprint measuring between 180 and 240 metres (590 and 790 ft), or the length of the stadium. The length of the race is uncertain, since tracks found at archeological sites, as well as literary evidence, provide conflicting measurements. Runners had to pass five stakes that divided the lanes: one stake at the start, another at the finish, and three stakes in between. A section of the stone starting line at Olympia, which has a groove for each foot The diaulos, or two-stade race, was introduced in 724 BC, during the 14th Olympic games. The race was a single lap of the stadium, approximately 400 metres (1,300 ft), and scholars debate whether or not the runners had individual "turning" posts for the return leg of the race, or whether all the runners approached a common post, turned, and then raced back to the starting line.

third foot race, the dolichos, was introduced in 720 BC. Accounts of the race present conflicting evidence as to the length of the dolichos; however, the length of the race was 18–24 laps, or about three miles (5 km). The event was run similarly to modern marathons—the runners would begin and end their event in the stadium proper, but the race course would wind its way through the Olympic grounds. The course often would flank important shrines and statues in the sanctuary, passing by the Nike statue by the temple of Zeus before returning to the stadium. The last running event added to the Olympic program was the hoplitodromos, or "Hoplite race", introduced in 520 BC and traditionally run as the last race of the Olympic Games. The runners would run either a single or double diaulos (approximately 400 or 800 yards) in full or partial armour, carrying a shield and additionally equipped either with greaves or a helmet.[39][40] As the armour weighed between 50 and 60 lb (27 kg), the hoplitodromos emulated the speed and stamina needed for warfare. Due to the weight of the armour, it was easy for runners to drop their shields or trip over fallen competitors. In a vase painting depicting the event, some runners are shown leaping over fallen shields. The course they used for these runs were made out of clay, with sand over the clay. Over the years, more events were added: boxing (pygme/pygmachia), wrestling (pale), and pankration, a fighting competition combining both elements. Archeology has shown little or no similarities between Ancient Greco-roman "pale" and any modern form of grappling including modern Greco-roman wrestling.[41] Other events include chariot racing, and several other running events (the diaulos, hippios, dolichos, and hoplitodromos), as well as a pentathlon, consisting of wrestling, stadion, long jump, javelin throw, and discus throw (the latter three were not separate events).