No single city owned the sanctuary of Apollo at Delphi. It was administered instead by the Amphictyonic League, a standing body drawing member peoples, traditionally counted as twelve, from across central and northern Greece, including Thessalians, Boeotians, Dorians, Ionians and others, each sending representatives called hieromnemones to a council that met twice a year, once at Delphi and once at the older amphictyonic center of Anthela near Thermopylae. The council managed the sanctuary's finances, oversaw its considerable dedicated treasuries, and organized the Pythian Games, the second most prestigious athletic and musical festival of the Greek world after the Olympics, held every four years in Apollo's honor.
Membership carried an oath, recorded by later writers including Aeschines, binding participants never to destroy a fellow member city, never to cut off its water supply even in wartime, and to move jointly against any state that violated the sanctuary's rights or plundered its property. The League functioned, in effect, as a rare piece of supra-polis religious and political machinery in a Greek world otherwise organized around fiercely independent city-states, precisely because Delphi's oracle mattered too much to any one of them to be left in a single city's hands.