Why was the Council of Nicea held in Nicea rather than Rome or Constantinople?

Background

There were about 1800 Christian Bishops in the Roman Empire in 325 AD (about 1,000 in the east and 800 in the west). We don't know exactly how many attended the first church council at Nicea. Eye witness accounts don't agree. What everyone agrees on is less than a quarter of the invitees made the trip. The Council itself lasted about a month so the discrepancy in attendee numbers could be due to when the counts were taken. Basically few from the east made the trip, and almost nobody from the west. This lack of attendance I've seen attributed to:

• Travel at the time was expensive, uncomfortable, and dangerous
• Bishops were mostly older men unsuited for travel
• Christianity teachings were not unified, and thus two bishops from different cities might disagree on fundamental teachings, which could also present dangerous situations for those in the minority.

Church History 101
Around 220 bishops attended, mostly from the eastern churches. Only around eight officials came from western churches - Rome sent only two presbyters.

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Historical Sources for Information on Nicean Church Counsel.

• Eusebius of Caesarea, Church History and Life of Constantine
• Socrates Scholasticus, Church History
• Sozomen, Church History
• Rufinus, Church History and
• Theodore, Church History

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Wikipedia
Eusebius of Caesarea counted more than 250, Athanasius of Alexandria counted 318,11 and Eustathius of Antioch estimated "about 270" (all three were present at the council). Later, Socrates Scholasticus recorded more than 300, and Evagrius, Hilary of Poitiers, Jerome, Dionysius Exiguus, and Rufinus recorded 318. This number 318 is preserved in the liturgies of the Eastern Orthodox Church and the Coptic Orthodox Church of Alexandria.

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Question: Why was the Council of Nicea held in Nicea rather than Rome or Constantinople?

Power doesn't travel. The Pagan emperor of Rome, Constantine called the bishops of the christian church to him. Constantine had a summer retreat at Nicea, a suburb of Byzantium(which Constantine would rename Constantinople a few years latter) and that's where he proposed to host the christian bishops from across the Roman Empire.

The Bishops of Rome and Constantinople(byzantium) would become preeminent leaders in the Christian Church due to their proximity to the Roman Emperors. They presided in the capitals of Rome(east and west). When the Roman Emperor had questions about christianity, they were the closest authority. This is how these bishops became preeminent. They were not the leaders of Christianity in 325AD that they would become. Christianity did not have central authority at that time. Christianity was just emerging from centuries of Roman persecution and was not centrally organized beyond bishops in most cities. Organization and Unity were the goals of the first church council. Goals which were not achieved.

Constantine called for the first church council, he hosted it, he presided over it, and he set the agenda. Constantine was looking for an expression of faith defining what it was to be Christian, because Constantine was interested in Unity. Constantine's major problem with the Christians is they disagreed on what it meant to be Christian. Without a unifying statement of belief they would never be the unifying force he envisioned to help solidify Rome.

Heretical teachings would be the first great challenge of the Christian Church. The early Christian Church was beset by many Heresies:

• Gnosticism - Jesus didn't die on the Cross.
• Marcionism - Two different Gods, hebrew god in old testament and the New Christian God.
• Montanism - Montanus's followers believed he was the holy ghost and called by God to set up his own organizational structure and doctrine for Christianity.
• Donatists - believed christians who recanted the faith in the face of persecution could not be forgiven and re-enter the church.
• Meletians - also concerned with lapsed christians being re-accepted into the faith
• Macedonians - (semi-arians), questioned the divinity of the holy ghost.
• Arianism - believe God the Father predates and created Jesus the son. Jesus was thus not eternal or coequal, but was made, not begotten.

Constantine fresh off the schism of Donatists, was horrified by all the different factions dividing and fracturing Christians. Which is why the Nicean Creed reads like a list of bullet items. Each line refutes an early Christian Heresy.

With strong lobbying and watchful eye from Constantine, who did not vote, the Nicean Creed got the majority of the 220-300 bishops in attendance. Still the the vast majority of Christian Bishops were not in attendance. By the time of Constantine's death 337AD, Nicean Christians had lost favor to Arians. Constantine would be baptized on his deathbed by an Arian Bishop (Eusebius of Nicomedia) previously excommunicated and exiled by the Church under Nicean leadership. None of the next six Roman Emperors would be Nicean Christians which would become a heretical teaching. The creed itself was re-written at the First Council of Constantinople assembled by the roman Emperor Theodosious; in 381 AD, to further clarify the divinity of Jesus and the holy ghost.

• Constantine II - Arian
• Constantius II - Arian
• Julian - Grew up Arian, rule as Roman Polytheist.
• Jovian - Neutral
• Valentinian I - Neutral
• Valens - Arian persecuted Niceans
• Theodosius I - Nicean persecuted Arians, became emperor 392AD.

Nicene Christianity would not return to favor until Theodosius 55 years after Constantine was baptized as an Arian on his death bed.