 The oldest extant work in which the word "Trinity" itself (Greek "Trias, triados") is used is Theophilus of Antioch's 2nd-century "To Autolycus".There it is used to refer to God, his word and his wisdom.The view that the Son was 'of the essence of the Father, God of God...very God of very God' was formally ratified at the First Council of Nicaea in 325 CE.