The term "Great Church" (Latin : ecclesia magna) is used in the historiography of early Christianity to mean the period of about 180 to 313, between that of primitive Christianity and that of the legalization of the Christian religion in the Roman Empire, corresponding closely to what is called the Ante-Nicene Period. "It has rightly been called the period of the Great Church, in view of its numerical growth, its constitutional development and its intense theological activity." 
The Great Church, also called the catholic (i.e., universal) Church,  has been defined also as meaning "the Church as defended by such as Ignatius of Antioch, Irenaeus of Lyons, Cyprian of Carthage, and Origen of Alexandria and characterized as possessing a single teaching and communion over and against the division of the sects, e.g., gnosticism, and the heresies". 
By the beginning of the fourth century, the Great Church already formed about 15% of the population of the Roman Empire and was ready, both numerically and structurally, for its role as the church of the empire, becoming the state religion of the Roman Empire in 380.  However, it would be wrong "to over-emphasize the new externals of the Church at the expense of historical continuity".  It was still the same Church.
Roger F. Olson says: "According to the Roman Catholic account of the history of Christian theology, the Great Church catholic and orthodox lived on from the apostles to today in the West and all bishops that remained in fellowship with the bishop of Rome have constituted its hierarchy";  or, as the Catholic Church itself has expressed it, "This Church constituted and organized in the world as a society, subsists in the Catholic Church, which is governed by the successor of Peter and by the Bishops in communion with him, although many elements of sanctification and of truth are found outside of its visible structure." 
The unbroken continuity of the Great Church is affirmed also by the Eastern Orthodox Church: "Orthodoxy regards the Great Church in antiquity (for most of the first millennium) as comprising, on one side, the Eastern Orthodox world (the Byzantine patriarchates presided over by the hierarch of the Church of Constantinople together with the Slavic Orthodox churches); and, on the other side, the Western Catholic Church, presided over by the hierarch of the Church of Rome." 
Lawrence S. Cunningham, and separately, Kugel and Greer state that Irenaeus's statement in Against Heresies Chapter X 1–2 (written c. 180 AD) is the first recorded reference to the existence of a "catholic Church" with a core set of shared beliefs as opposed to the ideas of dissident groups.   Irenaeus states: 
The Church, though dispersed through the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: ... As I have already observed, the Church, having received this preaching and this faith, although scattered throughout the whole world, yet, as if occupying but one house, carefully preserves it. ... For the churches which have been planted in Germany do not believe or hand down anything different, nor do those in Spain, nor those in Gaul, nor those in the East, nor those in Egypt, nor those in Libya, nor those which have been established in the central regions of the world. But as the son, that creature of God, is one and the same throughout the whole world, so also the preaching of the truth shineth everywhere, and enlightens all men that are willing to come to a knowledge of the truth.
Cunningham states that two points in Irenaeus' writing deserve attention. First, that Irenaeus distinguished the Church singular from "the churches" plural, and more importantly, Irenaeus holds that only in the larger singular Church does one find the truth handed down by the apostles of Christ. 
At the beginning of the 3rd century the Great Church that Irenaeus and Celsus had referred to had spread across a significant portion of the world, with most of its members living in cities (see early centers of Christianity).  The growth was less than uniform across the world. The Chronicle of Arbela stated that in 225 AD, there were 20 bishops in all of Persia, while at approximately the same time, surrounding areas of Rome had over 60 bishops.  But the Great Church of the 3rd century was not monolithic, consisting of a network of churches connected across cultural zones by lines of communication which at times included personal relationships. 
The Great Church grew in the 2nd century and entered the 3rd century mainly in two empires: the Roman and the Persian, with the network of bishops usually acting as the cohesive element across cultural zones.  In 313, the Edict of Milan ended the persecution of Christians, and by 380 the Great Church had gathered enough followers to become the State church of the Roman Empire by virtue of the Edict of Thessalonica. 
In Contra Celsum 5.59 and 5.61 the Church Father Origen mentions Celsus' late 2nd century use of the terms "church of the multitudes" or "great church" to refer to the emerging consensus traditions among Christians at the time, as Christianity was taking shape.  
In the 4th century, as Saint Augustine commented on Psalm XXII, he interpreted the term to mean the whole world, writing: "The great Church, Brethren, what is it? Is a scanty portion of the earth the great Church? The great Church means the whole world."  Augustine continued to expound on how various churches all considered themselves "the great Church," but that only the whole world could be seen as the great Church. 
The epoch of the Great Church witnessed the development of key theological concepts which now form the fabric of the religious beliefs of the large majority of Christians. 
Relying on Scripture, prevailing mysticism and popular piety, Irenaeus formalized some of the attributes of God, writing in Against Heresies Book IV, Chapter 19: "His greatness lacks nothing, but contains all things."  Irenaeus also referred to the early use of the "Father, Son and Holy Spirit" formula which appeared as part of Christian Creeds, writing in Against Heresies (Book I Chapter X): 
The Church… believes in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit.
Around 213 AD in Adversus Praxeas (chapter 3) Tertullian provided a formal representation of the concept of the Trinity, i.e., that God exists as one "substance" but three "Persons": The Father, the Son and the Holy Spirit.   Tertullian also discussed how the Holy Spirit proceeds from the Father and the Son.  The First Council of Nicaea in 325 and later the First Council of Constantinople in 381 then formalized these elements. 
In 451, all the bishops of the Great Church were ordered to attend the Council of Chalcedon to discuss theological issues that had emerged.  This turned out to be a turning point at which the Western and Eastern churches parted ways based on seemingly small Christological differences, and began the fracturing of the claim to the term Great Church by both sides.   
Official Catholic publications, and other writers, sometimes consider that the concept of the "Great Church" can be found already in the Epistles of Paul, such as in "This is my rule in all the churches" (1 Corinthians 7:17) and in the Apostolic Fathers such as the letters of Ignatius of Antioch.  Exegesis has even located the ecclesia magna in the Latin Vulgate translations of the "great congregation" (kahal rab) of the Hebrew Bible.  This interpretation was also offered by Pope Benedict XVI,  and by Martin Luther. 
Dennis Minns (2010) considers that the concept of a "Great Church" was developed by polemical heresiologists such as Irenaeus.  The presentation of early Christian unity and orthodoxy (see Proto-orthodox Christianity), and counter presentation of groups such as those sects labelled "Gnostic", by early heresiologists such as Irenaeus is questioned by modern historians. 
Roger E. Olson (1999) uses the term to refer to the Great Church at the time of the Council of Chalcedon (451) when the Patriarch of Constantinople and Bishop of Rome were in fellowship with each other. 
The term is contrasted with Jewish Christians who came to be more and more clearly separated from the Great Church.  Wilhelm Schneemelcher and others writing on New Testament Apocrypha distinguish writings as being sectarian or from the Great Church.  
Gabriele Waste (2005) is among German scholars using similar references, where the "Große Kirche" ("Great Church") is defined as "Ecclesia ex gentibus" (Church of the Gentiles) in comparison to the "Ecclesia ex circumcisione" (Church of the Circumcision). 
In the anglophone world, Bruce J. Malina (1976) contrasted what he calls "Christian Judaism" (usually termed "Jewish Christianity") with "the historically perceived orthodox Christianity that undergirds the ideology of the emergent Great Church."  
In francophone scholarship, the term Grande Église (Latin: Ecclesia magna) has also been equated with the "more hellenized" as opposed to "Judaizing" sections of the early church,  and the Bar Kokhba revolt is seen as a definitive stage in the separation between Judaism and the Christianity of the "Grande Église".  Those stressing this binary view of early Christianity include Simon Claude Mimouni and François Blanchetière.
Gnosticism is a collection of religious ideas and systems which coalesced in the late 1st century AD among Jewish and early Christian sects. These various groups emphasized personal spiritual knowledge (gnosis) above the orthodox teachings, traditions, and authority of religious institutions. Gnostic cosmogony generally presents a distinction between a supreme, hidden God and a malevolent lesser divinity who is responsible for creating the material universe. Consequently, Gnostics considered material existence flawed or evil, and held the principal element of salvation to be direct knowledge of the hidden divinity, attained via mystical or esoteric insight. Many Gnostic texts deal not in concepts of sin and repentance, but with illusion and enlightenment.
The history of Christianity concerns the Christian religion, Christian countries, and the Christians with their various denominations, from the 1st century to the present. Christianity originated with the ministry of Jesus, a Jewish teacher and healer who proclaimed the imminent Kingdom of God and was crucified c. AD 30–33 in Jerusalem in the Roman province of Judea. His followers believe that, according to the Gospels, he was the Son of God and that he died for the forgiveness of sins and was raised from the dead and exalted by God, and will return soon at the inception of God's kingdom.
Irenaeus was a Greek bishop noted for his role in guiding and expanding Christian communities in the southern regions of present-day France and, more widely, for the development of Christian theology by combating heterodox or Gnostic interpretations of Scripture as heresy and defining the Catholic and Orthodox doctrines of the Apostolic Churches. Originating from Smyrna, he had seen and heard the preaching of Polycarp, who in turn was said to have heard John the Evangelist, and thus was the last-known living connection with the Apostles.
Polycarp was a Christian bishop of Smyrna. According to the Martyrdom of Polycarp, he died a martyr, bound and burned at the stake, then stabbed when the fire failed to consume his body. Polycarp is regarded as a saint and Church Father in the Catholic, Eastern Orthodox, Oriental Orthodox, Anglican, and Lutheran churches.
Ebionites as a term refers to a Jewish Christian sect, which viewed poverty as a blessing, that existed during the early centuries of the Common Era. The Ebionites embraced an adoptionist Christology, thus understanding Jesus of Nazareth as a mere man who, by virtue of his righteousness in following the Law of Moses, was chosen by God to be the messianic "prophet like Moses". A majority of the Ebionites rejected as heresies the Orthodox Christian beliefs in Jesus' divinity, virgin birth and substitutionary atonement; and therefore maintained that Jesus was born the natural son of Joseph and Mary, sought to abolish animal sacrifices by prophetic proclamation, and died as a martyr in order to move all Israel to repentance.
Orthodoxy is adherence to correct or accepted creeds, especially in religion.
In ecclesiology, the Christian Church is what different Christian denominations conceive of as being the true body of Christians or the original institution established by Jesus. "Christian Church" has also been used in academia as a synonym for Christianity, despite the fact that it is composed of multiple churches or denominations, many of which hold a doctrinal claim of being the "one true church", to the exclusion of the others.
Cerinthus was an early Gnostic, who was prominent as a heresiarch in the view of the early Church Fathers. Contrary to the Church Fathers, he used the Gospel of Cerinthus, and denied that the Supreme God made the physical world. In Cerinthus' interpretation, the Christ descended upon Jesus at baptism and guided him in ministry and the performing of miracles, but left him at the crucifixion. Similarly to the Ebionites, he maintained that Jesus was not born of a virgin, but was a mere man, the biological son of Mary and Joseph.
An apostolic see is an episcopal see whose foundation is attributed to one or more of the apostles of Jesus or to one of their close associates. In Catholicism the phrase, preceded by the definite article and usually capitalized, refers to the See of Rome.
The Apostolic Fathers, also known as the Ante-Nicene Fathers, were core Christian theologians among the Church Fathers who lived in the 1st and 2nd centuries AD who are believed to have personally known some of the Twelve Apostles or to have been significantly influenced by them. Their writings, though widely circulated in early Christianity, were not included in the canon of the New Testament. Many of the writings derive from the same time period and geographical location as other works of early Christian literature which came to be part of the New Testament.
Quartodecimanism is the practice of celebrating Easter on the 14th of Nisan being on whatever day of the week, practicing Easter around the same time as the Passover was to be kept. Quartodecimanism caused controversy in the Church over if Easter should be celebrated on a certain day of the week or at the same time as the Jews would sacrifice the lamb.
Pauline Christianity or Pauline theology, otherwise referred to as Gentile Christianity, is the theology and form of Christianity which developed from the beliefs and doctrines espoused by the Hellenistic-Jewish Apostle Paul through his writings and those New Testament writings traditionally attributed to him. Paul's beliefs were rooted in the earliest Jewish Christianity, but deviated from this Jewish Christianity in their emphasis on inclusion of the Gentiles into God's New Covenant, and his rejection of circumcision as an unnecessary token of upholding the Mosaic Law.
Heresy in Christianity denotes the formal denial or doubt of a core doctrine of the Christian faith as defined by one or more of the Christian churches.
The doctrine of the Trinity, considered the core of Christian theology by Trinitarians, is the result of continuous exploration by the church of the biblical data, thrashed out in debate and treatises, eventually formulated at the First Council of Nicaea in AD 325 in a way they believe is consistent with the biblical witness, and further refined in later councils and writings. The most widely recognized Biblical foundations for the doctrine's formulation are in the Gospel of John.
Against Heresies, sometimes referred to by its Latin title Adversus Haereses, is a work of Christian theology written in Greek about the year 180 by Irenaeus, the bishop of Lugdunum.
Heresy is any belief or theory that is strongly at variance with established beliefs or customs, in particular the accepted beliefs of a church or religious organization. The term is usually used in reference to violations of important religious teachings, but is also used of views strongly opposed to any generally accepted ideas. A heretic is a proponent of heresy.
Christianity in the ante-Nicene period was the time in Christian history up to the First Council of Nicaea. This article covers the period following the Apostolic Age of the first century, c. 100 AD, to Nicaea in 325 AD.
Early Christianity spread from the Levant, across the Roman Empire, and beyond. Originally, this progression was closely connected to already established Jewish centers in the Holy Land and the Jewish diaspora. The first followers of Christianity were Jews or proselytes, commonly referred to as Jewish Christians and God-fearers.
Historiography of early Christianity is the study of historical writings about early Christianity, which is the period before the First Council of Nicaea in 325. Historians have used a variety of sources and methods in exploring and describing Christianity during this time.
Traditionally in Christianity, orthodoxy and heresy have been viewed in relation to the "orthodoxy" as an authentic lineage of tradition. Other forms of Christianity were viewed as deviant streams of thought and therefore "heterodox", or heretical. This view was challenged by the publication of Walter Bauer's Rechtgläubigkeit und Ketzerei im ältesten Christentum in 1934. Bauer endeavored to rethink Early Christianity historically, independent from the views of the current church. He stated that the 2nd-century church was very diverse and included many "heretical" groups that had an equal claim to apostolic tradition. Bauer interpreted the struggle between the orthodox and heterodox to be the "mainstream" Church of Rome struggling to attain dominance. He presented Edessa and Egypt as places where the "orthodoxy" of Rome had little influence during the 2nd century. As he saw it, the theological thought of the "Orient" at the time would later be labeled "heresy". The response by modern scholars has been mixed. Some scholars clearly support Bauer's conclusions and others express concerns about his "attacking [of] orthodox sources with inquisitional zeal and exploiting to a nearly absurd extent the argument from silence." However, modern scholars have critiqued and updated Bauer's model.