Laudator Temporis Acti

Robin Waterfield, Olympia: The Story of the Ancient Olympics (London: Head of Zeus, 2018), page number unknown (from chapter 1):

Whether they were rich or poor, and whether they came from one of the few great states or one of the many that were small and obscure, everyone at Olympia recognized themselves as kin. The games were an affirmation of Greekness that was particularly important for those visiting from overseas or the fringes of the Greek world. When the fifth-century-BCE historian Herodotus of Halicarnassus said that one of the things that bound all Greeks together, wherever they lived, was their common sanctuaries and festivals, he was thinking of the Olympic festival and others like it.⁵ A shared religious festival such as the Olympics gave the Greeks a chance to recognize their cultural unity — even though, as we shall see, it often did little to disguise their political disunity.

Greeks lived not just in the country that is nowadays called 'Greece', but also in separate states all over the Mediterranean and Black Sea coastlines. From about the middle of the fifth century onwards, judges were appointed at Olympia — they were called the Hellanodikai, the 'judges of the Greeks' — and one of their jobs was to make sure that all contestants were genuinely Greek, full citizens of their states (in particular, not slaves) and of good standing in their states. Greekness remained a prerequisite for several centuries, until from the end of the third century BCE the rule was obsequiously bent for Romans, the new masters of the Mediterranean world (though in fact they entered only the equestrian events, and left the rest to Greeks).

5 Herodotus, Histories, 8.144