Constantine NEVER converted to Christianity.

Emperor Constantine, before he was emperor, grew up during the reign of his father Constantine Chlorus, who was a devout follower of the cult called Sol Invictus, the "Unconquered Sun". This cult was made an official cult of the Roman Empire in 274AD by emperor Aurelian. Constantine's mother, Empress Helena, was a devout Christian. Constantine, however, took after his father, and became a follower of Sol Invictus aka Mithras, Apollo, Phoebus, Ra, etc. Mithras, or Mehr, is an Iranian Zoroastrian angelic divinity of covenant, light, oath as well as justice and an all-seeing protector of Truth, the guardian of cattle, the harvest, and of water. Apollo is a god of archery, music and dance, truth and prophecy, healing and diseases, the sun and light, poetry, and much more. Phoebus is the Roman name of Apollo. Ra was seen as the ruler of the world, the god of the sun, order, kings, and the sky.
In every religion that has a sun god, the sun is seen as the bestower of light and life to the totality of the cosmos; with his unblinking, all-seeing eye, he is the stern guarantor of justice; with the almost universal connection of light with enlightenment or illumination, and is the source of wisdom. Kings ruled by the power of the sun and claimed descent from the sun. Solar deities, gods personifying the sun, are sovereign and all-seeing.

Constantine associated his victory over Maxentius in 312AD with the power of the sun. He viewed Sol Invictus as very similar to the Christian God and he decided that Sol Invictus was the god of the Christians. His adoption of Christianity in the Roman Empire was a matter of political strategy, not religious conviction; he needed Christians on his side if he was going to keep control of his empire.

After his confessed conversion to Christianity, Constantine continued to mint coins with images of the sun god on them until 326AD at the earliest.



Sol Invictus behind Constantine





In 330AD, Constantine erected a column with himself at the top depicted as the sun god. This column became the center of the Forum of Constantine in the city of Byzantium, today known as the Cemberlitas Square in Istanbul.


The sign Constantine said God told him to conquer under is the Chi-Rho. However, this symbol is not a new symbol and appears on coins from Ptolemaic Kingdom of Egypt(Greek ruled) that were minted from 246-222BC.
It can be seen underneath the eagle...

Another Egyptian coin

And another


Also the symbol can be interpreted as a simple combination of two Nordic runes.
and
The former is "wunjo", meaning "joy" or "bliss". The latter is "gebo", meaning "sacrifice". A very clever combination and rendition of runes to say the least. These runes were first created in the 2nd century, before the time of Constantine.

All of this only begs questions about the truthfulness of Constantine's apparent conversion to Christianity. Why would he continue to mint coins with the sun god on them and his face on the other side? Why would he erect columns with statues of himself depicted as a sun god on top? Why would he recycle pagan symbols as Christian symbols and say he saw them in a vision?
Not only are these questions raised, but others are too, especially about the Roman Catholic Church and the Eastern Orthodox Church, both of which claim to be the true Christian Church, but based that on the same history and the claim that Constantine the Great converted to Christianity and turned the Roman Empire into a Christian nation. Both institutions use scripture as their forte in saying that Church has all the authority, 1 Timothy 3:15, however, how does one come to conclusion that said Church is the true Church? What is the authority on what is the true Church, the Church that Jesus Christ established? It could only be God, and His word.
2 Timothy 3:16-17 says,
16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
17 That the man of God may be perfect, thoroughly furnished unto all good works.

This means scripture is God breathed and is our final authority and our guide for judging all things.
1 Corinthians 2:15 But he that is spiritual judgeth all things, yet he himself is judged of no man.

And with that we can be certain that the evidence given, and this is only but a small amount of evidence, there is inconsistency with the claims of the Church of Rome, Catholic and Orthodox.