Panionia the great national festival of the Ionians. in honor of Poseidon (Neptune), the god whom they specially revered. On this occasion a bull was sacrificed, and if the animal roared during the process of killing it was regarded as pleasing to the deity. The sacrifices were performed by a young man of Priene, who was chosen for the purpose with the title of king. The festival was held on Mount Mycale, where stood the Panionium, or temple of Poseidon Heliconius.