Fifty years earlier, Irenaeus and Clement of Alexandria are said to have Trinitarian teachings in their writings. Justin Martyr, who died in AD157, is also said to mention the Trinity.  

It has been stated that Ignatius, who was born in AD33, has in his Didache "the Trinitarian formula of Matthew 28:19 in its instructions for baptism."  http://www.kencollins.com/explanations/why-07.htm

It is important to note on this last point that this 'formula' as it is called in Roman Catholic writings is said to be an interpolation, or added to the text.   However, this is disputed by many.   If it was added by the Catholic Church as a baptismal formula, they are correct in saying it is the Trinitarian formula for baptism, however, this does not make it a formula for those who are not Roman Catholics.  The apostles baptised in the name of Jesus.  See Acts 2:38.


Two things must be stated.  

1. The Nicaean Council was not only about whether the Son was like God or the same as God, but other doctrines and canons were discussed and voted upon.   Making Easter a Sunday was also decided at the council.

2. The doctrine of the Trinity did not originate with the Council of Nicaea or Constantinople. A full century earlier, Tertullian wrote a lengthy defense of the Trinity.

We believe in one God, the Father Almighty, maker of all things visible and invisible; and in one Lord Jesus Christ, the Son of God, the only-begotten of his Father, of the substance of the Father, God of God, Light of Light, very God of very God, begotten (γεννηθέντα), not made, being of one substance (ὁμοούσιον, consubstantialem) with the Father. By whom all things were made, both which be in heaven and in earth. Who for us men and for our salvation came down [from heaven] and was incarnate and was made man. He suffered and the third day he rose again, and ascended into heaven. And he shall come again to judge both the quick and the dead. And [we believe] in the Holy Ghost. And whosoever shall say that there was a time when the Son of God was not (ἤν ποτε ὅτε οὐκ ἦν), or that before he was begotten he was not, or that he was made of things that were not, or that he is of a different substance or essence [from the Father] or that he is a creature, or subject to change or conversion — all that so say, the Catholic and Apostolic Church anathematizes them.  wikipedia  (Including the sentence relating to the Holy Spirit from Constantinople)

An original Nicene Creed

"During the early fourth century, Arius was presbyter (elder, priest) in charge of a parish church in Alexandria, Egypt.   When the bishop of the city attempted to explain ‘the unity of the Holy Trinity’, Arius dissented, sharing his views with others.    Bishop Alexander (Catholic bishop of Alexandria) called a small synod of presbyters to discuss the question.  Both sides claimed victory and the controversy grew."  Two Republics. A.T. Jones p332.   

Eventually many bishops and clergy agreed with Arius, and they in turn taught the people.   Finally Alexander called a council of 100 bishops, most of whom supported his view.  

At the council, Arius was commanded to abandon his views and adopt the beliefs of Alexander. He refused and was excommunicated with all who believed as he did.    

The Arian bishops and clergy sent a statement of their views to other bishops, asking for support to be received back into communion.   Bishop Alexander also sent circular letters to the bishops.

Arius began to write songs that set forth his views, putting them in a book entitled ‘Thalia’, meaning ‘Songs of Joy’.    This book became so popular, it was not long before hundreds were singing his songs.

Thus the controversy spread.

The main difference in belief was the relationship of the Son to the Father.

Bishop Alexander said:   “We believe, as is taught by the Church, in an  only  unbegotten Father, Who of His being  has no cause, immutable and invariable… and in one Lord Jesus Christ, the only-begotten Son of God, begotten not out of that which is not, but of the Father…

And He is Father from the continual presence of the Son… for He did not beget His only Son in time, or in any interval of time, nor out of that which had no previous existence.”   Ecclestiastical History, Theodoret. Bk 1. Ch iv.  Written by Bishop Alexander.

Arius said: “But we say and believe… that the Son is not unbegotten…  and that before He was begotten, or created, or purposed, or established, He was not.   For He was not unbegotten.    We are persecuted, because we say that the Son has a beginning, but that God is without beginning…”  Ibid Bk 1. Ch 4.  Written by Bishop of Nicomedia, an Arian.

The dispute became a debate as to whether the Son was of the same substance of the Father or of like substance with the Father.  

A council was called in AD325 at Nicaea, composing 318 bishops, of whom eighteen were Arian.  After much noisy disputing and argument, the controversy was resolved by the addition of the Greek word homoousious to a creed.  The word, meaning ‘same substance’ or ‘consubstantial’, expressed the Catholic belief in more than one person inhabiting the same substance without division or separation.    This became the original Nicene Creed.  (Another word that expressed the belief of Arius more clearly was homoiousious, ‘like substance’, although the difference was certainly not absolute)

The Arian bishops were asked to sign the corrected creed;  seventeen refused, but when commanded under penalty of banishment, twelve succumbed.   Eusebius of Caesarea, a favourite counsellor of Constantine, and also an Arian, consulted the emperor to explain the meaning of homoousious.   

The emperor quietly told him that it could be understood as homoiousious.  Those in the council who heard the reply, mockingly called Constantine a heretic, bringing laughter to the lips of many.    Eusebius signed, believing the emperor’s explanation.   

The number gradually dwindled down to four who refused to sign, but when banishment was clearly the alternative, two yielded.  The other two absolutely refused, and were banished with Arius. 

However, the Council of Nicaea did not solve the problem. 

Those believing the teaching of Arius grew and multiplied.  

The Nicean Creed was not immediately accepted by all, but within 50 years it became the accepted creed of the church.

"Ever since Nicea, a belief in the deity of Christ has been an essential fundamental of the Faith for all orthodox Christians. It is the belief today of the Greek Orthodox Church, the Roman Catholic Church, and of the churches of the Reformation (including the Baptists and Independents)." 
Brackets in quote  http://www.thirdmill.org/newfiles/jac_arnold/CH.Arnold.CH.13.html

Two years later, at the request of his dying Arian sister, Constantine restored Arius, and the two others banished with him. He banished Athanasius, then bishop of Alexandria for refusing to reinstate Arius.  


The Nicene Creed:


We can take our beliefs from the records of church history or we can believe the Word of God.


What will you decide?

Nicaea

The Council of Nicaea

The John Ryland Library. Manchester. UK