On what grounds was Arius refuted at the First Council of Nicaea?

What proof does anyone have that Christ was the same and identical as the one He called "Father" even when Christ himself said in John 14:10... > Don't you believe that I am in the Father, and that the Father is in > me? The words I say to you I do not speak on my own authority. Rather, > it is the Father, living in me, who is doing his work. (NIV) Yes, Jesus was the Son of God although He never Himself said as much; He said He was "the Son of Man" only (for, I believe, He was truly humble in nature). But how can *men* know exactly what Christ was without experiencing a gnosis of some kind? The very fact that they proclaimed to have known what *exactly* Christ was precludes any so-called "evidence" they put forth. On the other hand, Constantine was a politician/stateman and a duplicitous pagan most of his life. How could he and his associates *possibly know* what exactly Christ was and make an absolute statement that He was identical to the one He called "Father" and call the Arian/Arius view a heresy?