Mithra Influence on Christianity

A Mystery-Religion was a religion of Redemption which professed to remove estrangement between man and God, to procure forgiveness of sins, to furnish mediation. Means of purification and formulae of access to God, and acclamations of confidence and victory were the part of the apparatus of every Mystery.  All the Mystery-gods were primarily savior-gods.  They prescribed a sacramental efficacy which atoned for a man's past, gave him comfort in the present, a participation in the divine life, and assured the believer that they would come into a hereafter of such dazzling splendor that the trials and conflicts of this earthly existence were dwarfed into insignificance.  One of the longest lived Mystery religions was the worship of Mithra.
In Genesis 10:9 there is mention of Nimrod 'the mighty hunter before the Lord'. This was the beginning of the 'son of the sun god' theme which became the mainstay of early pagan religions.  This pagan god was originally an Indo-Iranian cult god who later became known as Demuzi, or Tammuz of the Babylonians.  The Assyrians worshipped their main god Bel who later became known as Ormazd and his consort, Innana, who the Babylonians called Ishter, the virgin 'Queen of Heaven.'  Their child was the 'son of the sun-god', Demuzi or Tammuz.  Tammuz was to become the cult god, Mithra. Mithra was regarded as the Lord of light, truth, integrity, and the god of solemn oaths and contracts.  This cult was a secret males only cult, leaving the women with Ishter, the Queen of Heaven and the moon goddess to worship.  The Egyptians changed the name of Mithra to Aton for their practices.   Plutarch, a Greek historian (46-125AD) recorded that the cult god Mithra was brought into Rome by pirates from a Ciliciain clan in eastern Turkey. In 67BC Mithra worshippers held their first convention lead by the Roman commander Pompey.  Mithra became the soldiers god.  To them Mithra promised victories to the faithful who continually offered sacrifices. The Roman Legion soldiers took their 'Mithra' with them throughout the Middle East, along the Rhine and Danube rivers, and finally into Britain.   Archeologist have found as many as 718 monuments or statues of Mithra at Ostia, and close to 300 in Rome. A Mithra shrine was uncovered under St. Paul's cathedral.   Those of the legionary standing guard would lift their spears and salute:

Rome is above the nations, but thou art over all.
Now the names are answered, and the guards are marched away,
Mithras also a soldier, give us strength for the day.

Next would come a shout of victory:

SOL INVICTUS
(The Invincible Sun)

Faithful followers of Mithra included the Roman emperors Nero,Commodus, Septimus, Aurelian, Julian the Apostate, and Dioclethian.  In 307AD Dioclethian made worship of Mithras the main national religion declaring the 'son of the sun-god' to be Protector of the Empire.  Afterwards, Dioclethian persecuted the Christians.  In 312AD Constantine claims to have seen a portent in the sky prior to winning a battle and afterwards became 'converted to Christianity'. He caused all of the shrines dedicated to Mithra to be rededicated to Christ.  Actually, most of the tenants and doctrines of Mithra were transferred into the 'so called' Christian church.  In 321AD Constantine wrote:

'Constantine, Emperor Augustus, to Helidus.
On the venerable day of the sun let the magistrates, and the people residing in cities rest, let all workshops be closed.  In the country, however, persons engaged in agriculture may freely and lawfully continue their pursuits'.

The 'venerable day of the sun' was the special day of the week dedicated to the cult sun-god, Mithra as the first day of the week, Sun Day.  Since the emperor had made Christianity the state religion, for some, it meant no more than changing the name of Mithra to Christ, renaming their temples, and changing the day of worship from Saturday to Sunday. As subsequent emperors became hostile to the worship of Mithra, the worshippers were forced to 'go underground'.  The tables were turned and now they were the persecuted as 'the cult of the Persians'.
Sacraments of bread and wine were nothing new to Mithra worshippers.  The soldiers would leave bread out in the sun to absorb the sun's rays.  Afterwards, when they would eat the bread, they imagined themselves to therefore be ingesting the benefits of the sun and becoming one with it.
December 22/23 was regarded as time time of the sun's yearly death since this was the beginning of the winter solstice and the sun's weakest point.  Since the sun then 'returned' and became stronger after that, this was taken as the sun's 'rebirth'. Consequently, they declared a few days after that to be Mithra's birthday, December 25.  In Rome a week before December 25, there was a week of celebration while presents were exchanged.  The Romans called this period of time 'Saturnalia'.  December 25 was the most important date on the Babylonian calendar year.  Later this became 'christianized' to be Christ's birthday. 
The women weren't left out.  They worshipped the fertility goddess Ishtar, the Queen of heaven, or Magnus Mater.  They were worshipping the Moon goddess.  Monday was named after 'Moon day'.  At the end of March, at the first full moon of spring in the northern hemisphere, there was the celebration of human procreation. On this day, Rammuz, the forerunner of Mithra went down into the nether world and was rescued by his lover/mother,the fertility goddess, Ishtar, and an act of human procreation took place. Easter is a name for Ashteroth 'The Queen of Heaven'. Eggs and rabbits were the symbols of this fertility rite along with little round cakes decorated with crosses. The cakes were served with wine over which the priest pronounced a mystic formula.  Jeremiah 7:18 references this:

"The children gather wood, and the fathers kindle the fire, and the women knead their dough, to make cakes to the queen of heaven, and to pour out drink offerings unto other gods, that they may provoke me to anger."

(see also Jeremiah 44:17-19 & 25)
One of the signs of Mithra was the sign of the cross formed by the elliptic and the celestial equator.  This sign was put on the foreheads of new initiates after their baptism into the Mysteries of Mithra.