What stadium were the ancient Olympics held in?
The ancient Olympics were held at Olympia (near Elis, in the western Peloponnese, Greece). At first there was no stadium in the sense of a structure (stadion in Greek simply means "running-track"). The first stadium at Olympia was built about 550 BC, then remodelled in 500 BC with a sloped bank for spectators to stand on, and so on being re-built several times over nearly 900 years.
Eventually Olympia grew into a complex of temples, accommodations, and other facilities including a stadium for running, a hippodrome for horse-racing, a palaistra for wrestling, etc, etc.