Male Greek athletes, who were born free, participated in the ancient Olympics. They wore no clothes during their meets and ran barefooted. Scholars believe the type of clothing worn at the time would have restricted peak athletic performance.
Olympic festivals were so important that the Greeks imposed a Sacred Truce so athletes could freely travel. (In Greek, the word for truce - ekecheiria - means "holding of hands.") The words of the Truce were inscribed on a bronze discus, housed in the Temple of Hera, at Olympia. Its impact was significant.
While in effect, the truce suspended wars and death penalties, prevented armies from entering Elis and/or threatening the Games, and held legal disputes in abeyance. Sanctions were imposed against violators.
Women and girls could not participate as athletes in the ancient Olympic games. When equestrian events were added, women were allowed to own competing chariot teams and individual horses, but they could not ride the horses or guide the teams themselves. Pausanias (writing in the 2nd century A.D.) reports (at 5.8.11):
Afterwards they added races for chariots and pairs of foals, and for single foals with rider. It is said that the victors proclaimed were: for the chariot and pair, Belistiche, a woman from the seaboard of Macedonia...
Unmarried girls were allowed to watch the competition, but married women were absolutely forbidden on penalty of DEATH. Pausanias:
As you go from Scillus along the road to Olympia, before you cross the Alpheius, there is a mountain with high, precipitous cliffs. It is called Mount Typaeum. It is a law of Elis to cast down it any women who are caught present at the Olympic games, or even on the other side of the Alpheius, on the days prohibited to women.
A story is told of an exception to that rule. Pausanias continues:
However, they say that no woman has been caught, except Callipateira only....She, being a widow, disguised herself exactly like a gymnastic trainer, and brought her son to compete at Olympia. Peisirodus, for so her son was called, was victorious, and Callipateira, as she was jumping over the enclosure in which they keep the trainers shut up, bared her person. So her sex was discovered, but they let her go unpunished out of respect for her father, her brothers and her son, all of whom had been victorious at Olympia. But a law was passed that for the future trainers should strip before entering the arena.
Females, in honor of Hera, were allowed to run foot races in the Olympic stadium. However, these races (for girls, teenagers, and young women who likely wore knee-length tunics covering the left shoulder and breast) were not part of the ancient Olympic games, and the distance they ran (about 160 meters) was less than the distance for male competition (about 190 meters).
When Pierre de Coubertin launched the modern Olympics in 1896, he incorporated the ancient tradition of preventing females from participating in track and field events. That total ban lasted until the Amsterdam games of 1928. After Germany's Lina Radke collapsed that year, following her gold-medal run of the 800 meters, women were once again banned - this time from all races over 200 meters.
Those restrictions were not lifted until the 1960 games.