As the emperor of Rome, he was the head of religion for the roman empire at that time. There was no “Pope”. It seems that the lineage was created after adoption of Christianity as the official Roman religion. Man came up with the idea of a Pope.
Jesus said it best:
1 Then spake Jesus to the multitudes and to his disciples,
2 saying, The scribes and the Pharisees sit on Moses seat:
3 all things therefore whatsoever they bid you, these do and observe: but do not ye after their works; for they say, and do not.
4 Yea, they bind heavy burdens and grievous to be borne, and lay them on men’s shoulders; but they themselves will not move them with their finger.
5 But all their works they do to be seen of men: for they make broad their phylacteries, and enlarge the borders of their garments ,
6 and love the chief place at feasts, and the chief seats in the synagogues,
7 and the salutations in the marketplaces, and to be called of men, Rabbi.
8 But be not ye called Rabbi: for one is your teacher, and all ye are brethren.
9 And call no man your father on the earth: for one is your Father, even he who is in heaven.
10 Neither be ye called masters: for one is your master, even the Christ.
11 But he that is greatest among you shall be your servant. 12 And whosoever shall exalt himself shall be humbled; and whosoever shall humble himself shall be exalted.
The term is “Pontifex Maximus.”
Absolutely true. The Roman state religion was pagan both before and after Constantine. As has been patiently explained to you, Catholicism became the state religion a good 50 years after Constantine's death. And the definitive proclamation of you New Testament canon was another 20 years after that.
There was no “Pope”.
Of course there was. In fact, Constantine gave Pope Melchiades the estate which had formerly belonged to the family of Plautius Lateranus, which estate became the site of the cathedral of Rome, known today as "St. John Lateran".
Anybody can make up history and publish it. It sounds like that's what this book you're peddling consists of. Read Karl Keating's "Catholicism and Fundamentalism". You deserve to hear both sides of the story.