to define the relationship between the Father and the Son. After more than fifty years of debate, was recognised as the hallmark of orthodoxy, and was further developed into the formula of "three persons, one being". The Confession of the First Council of Nicaea, the Nicene Creed, said little about the Holy Spirit. At the First Council of Nicea (325) all attention was focused on the relationship between the Father and the Son, without making any similar statement about the Holy Spirit. In the words of the creed: First Council of Constantinople (381) Later, at the First Council of Constantinople (381), the Nicene Creed would be expanded, known as Niceno-Constantinopolitan Creed, by saying that the Holy Spirit is worshiped and glorified together with the Father and the Son (), suggesting that he was also consubstantial with them: The doctrine of the divinity and personality of the Holy Spirit was developed by Athanasius in the last decades of his life. He defended and refined the Nicene formula. By the end of the 4th century, under the leadership of Basil of Caesarea, Gregory of Nyssa, and Gregory of Nazianzus (the Cappadocian Fathers), the doctrine had reached substantially its current form. Middle Ages In the late 6th century, some Latin-speaking churches added the words "and from the Son" () to the description of the procession of the Holy Spirit, words that were not included in the text by either the Council of Nicaea or that of Constantinople. This was incorporated into the liturgical practice of Rome in 1014. eventually became one of the main causes for the East–West Schism in 1054, and the failures of the repeated union attempts. Gregory of Nazianzus would say of the Trinity, "No sooner do I conceive of the One than I am illumined by the splendour of the Three; no sooner do I distinguish Three than I am carried back into the One. When I think of any of the Three, I think of Him as the Whole, and my eyes are filled, and the greater part of what I am thinking escapes me. I cannot grasp the greatness of that One so as to attribute a greater greatness to the rest. When I contemplate the Three together, I see but one torch, and cannot divide or measure out the undivided light." Devotion to the Trinity centered in the French monasteries at Tours and Aniane where Benedict