Ancient Greek region and city-state, northwestern Peloponnese, Greece. Bounded by Achaea, Arcadia, Messenia, and the Ionian Sea, the region was known for its horse breeding and was the site of the Olympic Games. As an ally of Athens in the Peloponnesian War, Elis lost much of its territory. Later, by emphasizing the sanctity of the Olympic Games, it regained some land and even some independence after the Roman occupation of Greece (146 BC), only to disintegrate with the collapse of the Roman Empire. The modern locality contains the archaeological site of Olympia, scene of the games.