First Council of Constantinople in the context of "Catholicity"

In the history of Christianity, the first seven ecumenical councils are as follows: the First Council of Nicaea in 325, the First Council of Constantinople in 381, the Council of Ephesus in 431, the Council of Chalcedon in 451, the Second Council of Constantinople in 553, the Third Council of Constantinople from 680 to 681 and finally, the Second Council of Nicaea in 787.

These seven events represented an attempt by Church leaders to reach an orthodox consensus, restore peace and develop a unified Christendom. Among Eastern Christians the Eastern Orthodox, Oriental Orthodox, and Church of the East (Assyrian) churches and among Western Christians the Roman Catholic, Anglican, Utrecht and Polish National Old Catholic, and some Scandinavian Lutheran churches all trace the legitimacy of their clergy by apostolic succession back to this period and beyond, to the earlier period referred to as the Early Church.

The Four Marks of the Church, also known as the Attributes of the Church, describes four distinctive adjectives of traditional Christian ecclesiology as expressed in the Nicene Creed completed at the First Council of Constantinople in AD 381: "[We believe] in one, holy, catholic, and apostolic Church."

This ecumenical creed is today recited in the liturgies of the Eastern Orthodox Church, the Catholic Church (both Latin and Eastern Rites), the Oriental Orthodox Churches, the Assyrian Church of the East, the Moravian Church, the Lutheran Churches, the Methodist Churches, the Presbyterian Churches, the Anglican Communion, and by members of the Reformed Churches, although they interpret it in very different ways, and some Protestants alter the word "Catholic" in the creed, replacing it with the word "Christian".

Augustine of Hippo (/ɔːˈɡʌstɪn/ aw-GUST-in, US also /ˈɔːɡəstiːn/ AW-gə-steen; Latin: Aurelius Augustinus Hipponensis; 13 November 354 – 28 August 430) was a theologian and philosopher, the bishop of Hippo Regius from Thagaste in Numidia Cirtensis, (present-day Souk Ahras, Algeria). His writings deeply influenced the development of Western philosophy and Western Christianity, and he is viewed as one of the most important Church Fathers of the Latin Church in the Patristic Period. His many important works include The City of God, On Christian Doctrine, and Confessions.

According to his contemporary, Jerome of Stridon, Augustine "established anew the ancient Faith". In his youth he was drawn to the Manichaean faith, and later to the Hellenistic philosophy of Neoplatonism. After his conversion to Christianity and baptism in 386, Augustine developed his own approach to philosophy and theology, accommodating a variety of methods and perspectives. Believing the grace of Christ was indispensable to human freedom, he helped formulate the doctrine of original sin and made significant contributions to the development of just war theory. When the Western Roman Empire began to disintegrate, Augustine imagined the Church as a spiritual City of God, distinct from the material Earthly City. The segment of the Church that adhered to the concept of the Trinity as defined by the Council of Nicaea and the Council of Constantinople closely identified with Augustine's On the Trinity.

Nicene Christianity includes those Christian denominations that adhere to the teaching of the Nicene Creed, which was formulated at the First Council of Nicaea in AD 325 and amended at the First Council of Constantinople in AD 381. It encompasses the vast majority of today's Christian churches.

The Nicene Creed, also called the Creed of Constantinople, is the defining statement of belief of Nicene Christianity and in those Christian denominations that adhere to it.

The original Nicene Creed was first adopted at the First Council of Nicaea in 325. According to the traditional view, forwarded by the Council of Chalcedon of 451, the Creed was amended in 381 by the First Council of Constantinople as "consonant to the holy and great Synod of Nice." However, many scholars comment on these ancient Councils, saying "there is a failure of evidence" for this position since no one between the years of 381–451 thought of it in this light. Further, a creed "almost identical in form" was used as early as 374 by St. Epiphanius of Salamis. Nonetheless, the amended form is presently referred to as the Nicene Creed or the Niceno-Constantinopolitan Creed.

In the year before the First Council of Constantinople in 381, Nicene Christianity became the official religion of the Roman Empire when Theodosius I, emperor of the East, Gratian, emperor of the West, and Gratian's junior co-ruler Valentinian II issued the Edict of Thessalonica in 380, which recognized the catholic orthodoxy, as defined by the Council of Nicea, as the Roman Empire's state religion. Historians refer to this state-sponsored church using a variety of terms: the catholic church, the orthodox church, the imperial church, the Roman church, or the Byzantine church, with some also used for wider communions extending beyond the Roman Empire. The Eastern Orthodox Church, Oriental Orthodoxy, and the Catholic Church all claim to stand in continuity from the Nicene Christian church to which Theodosius granted recognition. Political differences between the Eastern Roman Empire and the Persian Sassanid Empire led to the separation of the Church of the East in 424. A doctrinal split within the imperial church led to the independence of early Oriental Orthodoxy, while the fall of the Western Roman Empire initiated the gradual separation between Eastern and Western Christianity, culminating in the East-West schism of 1054. The Western Church evolved into the Latin Catholic Church while the Eastern Church that remained under the patronage of the Eastern empire and evolved into the Greek Orthodox Church.

Earlier in the 4th century, following the Diocletianic Persecution of 303–313 and the Donatist controversy that arose in consequence, Constantine the Great had convened councils of bishops to define the orthodoxy of the Christian faith and to expand on earlier Christian councils. A series of ecumenical councils convened by successive Roman emperors met during the 4th and the 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the theological and christological doctrines of Arianism, Nestorianism, Miaphysitism, and Dyophysitism. In the 5th century, the Western Roman Empire decayed as a polity; invaders sacked Rome in 410 and in 455, and Odoacer, an Arian barbarian warlord, forced Romulus Augustus, the last nominal Western Emperor, to abdicate in 476. However, apart from the aforementioned schisms, the church as an institution persisted in communion, if not without tension, between the East and West. In the 6th century, the Byzantine armies of the Byzantine Emperor Justinian I recovered Italy and other regions of the Western Mediterranean shore. The Byzantine Empire soon lost most of these gains, but it held Rome, as part of the Exarchate of Ravenna, until 751, a period known in church history as the Byzantine Papacy. The early Muslim conquests of the 7th–9th centuries would begin a process of converting most of the then-Christian world in the Levant, Middle East, North Africa, regions of Southern Italy and the Iberian Peninsula to Islam, severely restricting the reach both of the Byzantine Empire and of its church. Christian missionary activity directed from the capital of Constantinople did not lead to a lasting expansion of the formal link between the church and the Byzantine emperor, since areas outside the Byzantine Empire's political and military control set up their own distinct churches, as in the case of Bulgaria in 919.

Filioque (/ˌfɪliˈoʊkwi, -kweɪ/ FIL-ee-OH-kwee, -⁠kway; Ecclesiastical Latin: [filiˈokwe]), a Latin term meaning "and from the Son", was added to the original Nicene Creed, and has been the subject of great controversy between Eastern and Western Christianity. The term refers to the Son, Jesus Christ, with the Father, as the one shared origin of the Holy Spirit. It is not in the original text of the Creed, attributed to the First Council of Constantinople (381), which says that the Holy Spirit proceeds "from the Father" (Greek: τὸ ἐκ του Πατρὸς ἐκπορευόμενον) without the addition "and the Son".

In the late 6th century, some Latin Churches added the words "and from the Son" (Filioque) to the description of the procession of the Holy Spirit, in what many Eastern Orthodox Christians have at a later stage argued is a violation of Canon VII of the Council of Ephesus, since the words were not included in the text by either the First Council of Nicaea or that of Constantinople. The inclusion was incorporated into the liturgical practice of Rome in 1014, but was rejected by Eastern Christianity.