The chiefs thus gathered together called this assembly the Amphictyonic Council, in honor of Amphictyon. After making plans to drive back the Thracians, they decided to meet once a year, either at Thermopylæ or at the temple at Delphi, to talk over all important matters.

From: H. A. Guerber, The Story of the Greeks; edited for this online publication, by ELLOPOS BLOG