He was born in Cappadocia, and was one of the 318 God-bearing Fathers who attended the First Ecumenical Council. At the council, Achillius took up a stone and said to the Arians, 'If Christ is a creature of God, as you say, tell oil to flow from this stone.' When the heretics kept silent, Achilleus went on, 'And if the Son of God is equal to the Father, as we believe, let oil flow from this stone,' at which oil flowed out. Returning to Larissa, the holy bishop cast down many pagan temples, built many churches, cast out many demons, and reposed in peace.