The temple believed to the Panionium was constructed next to the Carium about 540 BC. It took over the worship of Poseidon Heliconius, served as the meeting place of the Ionian League, and was the site of the religious festival and games ("panegyris") called the Panionia. The construction of this temple is a terminus post quem for the existence of the Ionian League, which as a constituted body had a name, the "koinon Iōnōn" ("common thing of the Ionians"), a "synedrion" ("place to sit down together") and a "boulē" ("council").