The area of Nemea has been inhabited since Early Neolithic times (6000 to 5000 BCE) and was settled throughout the Bronze Age with architectural remains, in particular rock-cut tombs, dating from the mid-16th century BCE to the 12th century BCE, the time of the Mycenaean civilization. The site reached its period of greatest importance from the 6th to 3rd centuries BCE when for around a month every two years, athletes and spectators gathered for the pan-Hellenic Games, held under the control of nearby Kleonai and then Argos. The Nemean Games became a sporting event to rank alongside the other three major pan-Hellenic athletic games held at Olympia, Isthmia, and Delphi.

The mythical origin of the Games is sometimes ascribed to Hercules who, after his first labor in which he had to kill the Nemean lion living in the caves of Mount Tritos above the site, established athletic games in honor of his father Zeus. A second and more likely mythological origin is the story of Opheltes. Lykourgos, the priest-king, had a son named Opheltes and seeking to protect his son he asked the Delphic oracle for advice. The response of the oracle was to prevent the baby from touching the ground until he had learned to walk. Opheltes was put under the care of a slave called Hypsipyle but while engaged fetching water for some passing champions on their way to Thebes, the unattended baby was fatally attacked by a snake while he slept in a bed of wild celery. Taking this as a bad omen, the champions organized funeral games to propitiate the gods and commemorate the unfortunate Opheltes. Thus the Nemean Games were born.

Architectural remains at the site are dominated by the impressive Temple of Zeus constructed c. 330 BCE. The ancient site has always been known; indeed three of the columns of the Temple of Zeus have never fallen down since they were originally erected. This was built on the site of an earlier temple from the 6th century BC which was destroyed by fire and from which blocks were used to construct the foundations of its replacement. The new temple was built of local limestone covered in fine marble-dust stucco with the inner sima in marble.