Pre-Christian Symbolism

Crucifixion, the Cross and the Fish (Ichthus)

Christianity adopted the cross later on.
Early Biblical texts claim that Christ was crucified by a stake, not cross:

• The church did not adopt the cross until about the 6th century (New Catholic Encyclopedia, vol. 4, p. 475).
• The word 'cross' was later substituted for the word 'stake' in the rewriting of the Christian text (Crosses In Tradition, W.W.Seymour N.Y. 1898).
• Christian archives record that the general use of the crucifix became ratified at the Sixth Ecumenical Council in 680 (Canon 82). The council decreed that 'the figure of a man fastened to a cross be now adopted'.
• This new church logo was later confirmed by Pope Hadrian I (772-795).

Early Christians never used the cross:

Although a stake called a stauros (the Greek term used in the earliest Bible writings but where English versions incorrectly translate it to "cross") got used to execute criminals, there exists not a shred of evidence that a Biblical stauros describes a cross or even a T-shape.

There occurs no cross in early Christian art before the middle of the 5th century, where it (probably) appears on a coin in a painting. The first clear crucifix appears in the late 7th century. Early Christians usually depicted their religion with a fish symbol (ichthus), dove, or bread of the Eucharist, but never Christ on a cross (or on a stick).

Crucified Bacchus - at About.com: Referring to the picture of the amulet of the crucified deity, it says

It is unusual as it depicts a crucified figure other than Christ at a time when similar images of Jesus were rare.

The page shows how the Roman God Bacchus, the Wine God, who was equivalent to Dionysus of the Greeks, was depicted on a cross, in the same pose as Christ would be later on (when the Church would adopt the Cross). It is known that such depictions of pagan Gods in the early Greco-Roman world completely determined how Christ was presented.
The Chi-Rho emblem, considered the first Christian Cross, was also a pre-Christian symbol: the original Chi-ro signified good fortune.

True Origin of Christian "FISH" Symbol:

"Ichthus," an acronym from the Greek, "Iesous Christos Theou Uios Soter," or "Jesus Christ the Son of God, Saviour."
... the acronym pertaining to Jesus Christ was a "rationale invented after the fact... Christians simply copied this pagan symbol along with many others." Ichthys was the offspring son of the ancient Sea goddess Atargatis, and was known in various mythic systems as Tirgata, Aphrodite, Pelagia or Delphine. The word also meant "womb" and "dolphin" in some tongues...

See more of its pre-Christian significance

Principal Christian Symbols: The Fish (Ichthus), Cross & Crucifix. These three symbols central to Christianity, are actually pre-Christian in origin. The Cross and Crucifix were known to the older European and other religions.
About the Fish symbol, this page states:

The fish symbol has been used for millennia worldwide as a religious symbol associated with the Pagan Great Mother Goddess.

Mother and Son

In the 4th century, the Isis cult was absorbed into the Christian Madonna cult. All the early pictures and statues of Madonna and child are actually those of Isis and her infant son, Horus.
This page has images of ancient sculptures of Isis with child and of Mary with child side-by-side.

It was the gnostic art that reproduced the Hathor-Meri and Horus of Egypt as the Virgin and child-Christ of Rome....
-- Gerald Massey, Egyptologist and poet

Biblical Origins In Ancient Egypt says about Hathor-Meri and Mary:

[The name] Mary ... derives from the Egyptian cow
...the Zodiac Sign of Taurus gave the Goddess Isis or Iusaas, her character of Meri the Cow, and so the name of Mary.

Gerald Massey in Ancient Egypt: "Iusa, the coming son, the second Atum, was born of Hathor-Iusãas, the cow-headed goddess, in the sign of the bull where the equinox rested from the year 6,465 to the year 4,310 B.C. In this sign the divine child was brought forth in the stable as a calf or a bullock. The lunar cow was in the stable of the solar bull, where the young babe was born and laid in a manger now as Horus or Iu, the calf. Mother and child might be and were portrayed in human form, but it is the cow that gives the name of "Meri", and but for the cow-headed Hathor-Meri there would have been no human Mary as a virgin-mother in the Jesus-legend.
Hathor-Meri was the mother of Horus, the Su in the "house of a thousand years", born in the stable or the manger of the bull.
...Iusãas, the mother of Iusa=Iusu, the Egyptian Jesus, was a form of Hathor-Meri, and was brought on in the cult of Rome as Mary, the mystical dove and mother of Iusu, now believed to have become historical."

Certainly in art the figure of Isis suckling the infant Horus is so like that of the Madonna and Child that it has sometimes received the adoration of ignorant Christians.
-- Sir James Frazer in The Golden Bough (1890)

Indeed: the revered Black Virgins found in churches and monasteries in Spain and Italy are in fact images of the Egyptian Goddess Isis and Her son Horus.

Virgin Mother

There was no virgin birth in Mark's gospel, for the simple reason that, according to scholarly consensus, it hadn't been invented yet.
-- Gospel Truth by R. Shorto

Link

[Early Church father] Irenaeus tells us that the MSS [manuscripts] of Matthew's gospel used ca. A.D. 185 by the Ebionites (the original Jewish Christians of Jerusalem) lacked the first two chapters - the chapters containing the imaginary genealogy of Jesus, the - virgin birth story, the wise men, and Herod's slaughter of the innocents. Small wonder that the earliest Christians did not believe the story about Mary and the angel!

Link
It also shows how there was no virgin birth in the geneology of the Syriacus Sinaiticus manuscripts, which was:

a third to fourth century document reflecting the state of the biblical text in the second century, before believers in the virgin birth myth had succeeded in altering all the gospel texts.

Same Link

Though the motif of a virgin mother giving birth to a divine son is common in many pre-Christian religions, especially those centred around solar deities, in Christianity this is actually a long-standing mistake based on an error in translation.
Bible scholars have long since abandoned a literal (mis)interpretation of Jesus' miraculous virgin-birth, which was supposedly prophesied in the Old Testament. However, this prophecy had been wrongly translated in an earlier Greek translation of the OT, the Septuagint.

The Greek priest who forged the "Gospel according to St. Matthew," having before him the false Septuagint translation of Isaiah ... [appeals] to the Septuagint translation of Isaiah vii, 14:

"Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel." (Matt. i, 23.)

...Honestly translated, the verse reads:

"Behold, the young woman has conceived -- [is with child) -- and beareth a son and calleth his name Immanuel."

...
Almah means simply a young woman, of marriageable age, whether married or not, or a virgin or not; in a broad general sense exactly like girl or maid in English..., without reference to or vouching for her technical virginity, which, in Hebrew, is always expressed by the word bethulah. But in the Septuagint translation into Greek, the Hebrew almah was erroneously rendered into the Greek parthenos, virgin...
-- The Septuagint and the "Virgin-Birth" fraud from Forgery in Christianity, by Joseph Wheless

About this passage in the Septuagint and the Hebrew version of the Old Testament:

...this passage has several problems, the largest hanging on the Hebrew word 'almah. Writing in Greek, the gospel author turned almah into parthenos , a word usually (but not always) meaning "virgin." In fact, he had a precedent for this; the Septuagint, a translation of the Old Testament used by Greek-speaking Jews of his day, did indeed use parthenos in the Isaiah passage.

But the Septuagint was for the most part a notoriously sloppy translation, and its version of Isaiah was generally more error-ridden than the rest. By the Middle Ages, the Jews had abandoned the Septuagint, and later Greek translations, by Aquila, Theodotion, Lucien and others, did not use the word parthenos. (The Septuagint, commonly known as the LXX, is still favored by Eastern Orthodox churches.)

Assuredly, the Hebrew Old Testament predating the Septuagint used 'almah...

From: A Virgin-Birth Prophecy?

"As early as the second century B.C.," says the distinguished Hebrew scholar and critic, Salomon Reinach, "the Jews perceived the error and pointed it out to the Greeks; but the Church knowingly persisted in the false reading, and for over fifteen centuries she has clung to her error." (Orpheus, p, 197.) The truth of this accusation of conscious persistence in known error through the centuries is proved by confession of St. Jerome, who made the celebrated Vulgate translation from the Hebrew into Latin, and intentionally "clung to the error," though Jerome well knew that it was an error and false; and thus he perpetuated through fifteen hundred years the myth of the "prophetic virgin birth" of Jesus called Christ.
--The Septuagint and the "Virgin-Birth" fraud from Forgery in Christianity, by Joseph Wheless

This continues to be an issue where Protestants and Catholics fail to see eye-to-eye, although in this case the Protestants are correct. That is why in many Bibles of today's Protestant denominations this error has been corrected. In other denominations, especially Catholicism, the false translation continues to be used. Most Protestants generally ignore this section, whereas Catholics continue to believe in the fiction that Mary was a virgin. Among the latter she retains her unique position of a virginal woman who nevertheless conceived, which gave her a divine status.

See more:
Immaculate Deception - The Mythical Virgin Mary

Reverence for Mary

There was no cult of the Virgin Mariam or Mary in the early centuries of the church

Link (making reference to the ERE, the Encyclopaedia of Religion and Ethics).

In fact, some quarters of the early Christian Church opposed the worship of Mariam as some kind of divine mother for the very fact that this was a pagan and therefore heretical practice:

The introduction of Mariolatry [revering Mary as divine] was some time later from the introduction in the Eastern rites. After the church was adopted by the Roman Empire the heathen practice or heresy was adopted and the practice is recorded by Epiphanius:

as heresy (Her, lxxix) that ‘certain women in Thrace, Scythia, and Arabia’ were in the habit of adoring the virgin as a goddess and offering to her a certain kind of cake [kollurida tina] whence he calls them ‘Collyridians’. Their practice (cf. Jer. 44:19) and the notion underlying it were undoubtedly relics of heathenism always familiar with female deities.

These cakes were made to the Queen of Heaven at her festival, the festival of Ishtar or Easter or Astarte, since long before the Babylonian captivity.
Epiphanius was adamant that Mary [or Mariam] was not to be worshipped.
...
The Trinitarians, particularly the Cappadocians, elevated Mary in response to the arguments of the non-Trinitarians later called Arians (cf. ERE, ibid., p. 476). They elevated Christ to God and then elevated ‘Mary’ as Mother of God and, hence, the Mother goddess and mother of the gods. These ideas were purely heathen and did not originate until the end of the fourth century. W R Ramsey argues that:

so early as the 5th. cent. the honour paid to the Virgin Mary at Ephesus was the recrudescence in a baptized form of the old pagan Anatolian worship of the Virgin Mother (Pauline and Other Studies, p. 126; cf. ERE, ibid., p. 477, n. 1).

The Virgin Mary was none other than Artemis or Diana of Ephesus that Paul so boldly opposed (Acts 19:24-35).

Link

See also: how it was only during the Church Council of Ephesus of 431 CE that Mary was proclaimed "mother of God", whilst the Nestorian Christians were opposed to it.
The Ebionites, the original Jewish followers of Jesus in Jerusalem, did not accept Mary's perpetual virginity either.

Models for the Christian Devil

Faunus (or Pan) was the Greco-Roman God of animals. The lower part of his body was that of a goat, and he had horns on his head. He represented kindly Nature which looked after animals. From Faunus comes the word fauna. In Greek mythology, the famous playful creatures that looked like him were called fauns and played on panflutes. It was hard to wean away the population from this popular and benevolent God, so Christianity shaped the Devil in his likeness: horns, hoofs and all.
In a similar manner, snakes were revered in Ireland and throughout Europe and Asia. The Christian myth of St. Patrick who chased away the snakes from Ireland (where real snakes were pretty scarce on the ground) tells of how the reverence of snakes was ended there: with the priests driven off and the population turning their backs on their past. Similarly, in mainland Europe, the Devil became increasingly associated with the appearance of a serpent. This slowly taught the European and west Asian converts to fear and loathe their former deities or animal spirits.

Pre-Christian festivals, holy days and terms for God

This replacement phenomenon, where a heathen festival is replaced by one with Christian names is seen in a number of pagan or heathen festivals. In line with the Mother goddess and Heavenly Virgin theology, the Festival of Diana was ousted by the Festival of the Assumption of the Virgin in August. Like changes were the pagan Parilia in April, which was replaced by the feast of St George. The midsummer water festival in June, was replaced by the festival of St John the Baptist. Each has connection with the typology it replaced. The Feast of All Souls in November is the ancient heathen Feast of the Dead. The Nativity of Christ replaced that of the Sun. The Festival of Easter is simply the feast of the Phrygian god Attis at the vernal equinox. It should also be remembered that the Phrygians were the source of the Mithras system and the Mystery cults generally...

Link

Easter

This was both a common Goddess (fertility) festival as well as a festival celebrating the death and resurrection of many Gods.

• In the Roman Empire, a Mithraic feast involving the eating of the Paschal lamb was celebrated at the time that Easter is held today. The Mithraic origins thereof made the Church try to suppress the associations of Jesus with the lamb in the 7th century.
• In the near-east, it was the festival of Goddess Ishtar that led to the Easter celebration and name:

  the Babylonian Goddess Ishtar, and her consort Tammuz. It is from their legend that we get the name for the annual celebration of the resurrection of Christ- Easter, a name of the Goddess Ishtar.

  Link
  Corresponding to Ishtar of Babylon, there was the Phoenician Astarte, both of whose fertility festivals were held during the present-day Easter period and led to the name Easter. The consorts of these fertility Goddesses were Gods whose death and resurrection were celebrated at Easter in pre-Christian times until the early Christian era.
  Similarly, the lover of the Greek Goddess Aphrodite (Roman Venus) was called Adonis and corresponded with the Phoenician God of the same name and the Babylonian Tammuz. Like them, Adonis was also a yearly resurrecting saviour-God. Therefore in pre-Christian Greece, Easter celebrated the Resurrection of Adonis at the time Jesus' Resurrection is observed now.

  Now the Easter rites still observed in Greece, Sicily and Southern Italy bear in some respects a striking resemblance to the rites of Adonis and I have suggested that the Church may have consciously adapted the new festival to its heathen predecessor for the sake of winning souls to Christ.
  -- Sir James Frazer, The Golden Bough

  Yet, as is known, souls to Christ were won in the Mediterranean (as elsewhere) by violence and force, not by inculturation. It was merely to prevent the converts from reverting to their old Gods during the popular pagan festivals that these were turned into 'Christian' feasts instead.
• Many think it possible that Eostre (Eastre) - the Anglo-Saxon name of a Teutonic goddess of spring and, like Isthar, of fertility too - might have led to the name of Easter, at least in the northern countries:

  Pagan Anglo-Saxons made offerings of colored eggs to her at the Vernal Equinox. They placed them at graves especially, probably as a charm of rebirth. (Egyptians and Greeks were also known to place eggs at gravesites).

  Link

  Eastre, the Anglo-Saxon name of a Teutonic goddess of spring and fertility, to whom people dedicated a month corresponding to April. People celebrated her festival on the day of the vernal equinox. The tradition of Eastre survive in the Easter rabbit, a symbol of fertility, and in colored easter eggs, originally painted with bright colors to represent the sunlight of spring, and used in Easter-egg rolling contests or given as gifts. Even the early Egyptians and Persians dyed eggs in spring colors and gave them to friends.

  Link

  The Catholic Encyclopedia, 1909:
  "The custom [of easter eggs] may have its origin in paganism, for a great many pagan customs, celebrating the return of spring, gravitated to Easter. The egg is the emblem of the germinating life of early spring.
  ...The Easter Rabbit lays the eggs, for which reason they are hidden in a nest or in the garden. The rabbit is a pagan symbol and has always been an emblem of fertility (Simrock, Mythologie, 551)."

• Though it is the oldest Christian festival, its observance started much later than one might think. The earliest known Christian celebration of "Easter" occurred between the 2nd and 4th centuries, and went under the name of Pasch, derived from Hebrew Pesah (the Jewish Passover feast). Back then, both the death and resurrection of Jesus were observed together. Today, this has changed to take place on two separate days (Good Friday and Easter Sunday).
  Instead of Easter, what Christians ought to be celebrating is the Jewish festival of Passover:

  Christians celebrate the annual festival commemorating the alleged resurrection of Jesus between March 22 and April 25.
  ...The Jews celebrate "Passover" at around this time, from an Exodus story where God passes over the "chosen ones" on his way to kill the firstborn of Egypt (Exodus 11, 12).

  Link
  As one of the many Christian denominations and sites admits:

  The Universal Oxford Dictionary gives the method for determining Easter Sunday or Easter day which is the true Day of the Sun as Easter.

  It is observed on the first Sunday after the calendar full moon, i.e. the 14th day of the calendar moon - which happens on or next after 21 March. Applied colloq. to the week commencing Easter Sunday (1964 print, p. 579).

  This is the rule for determining the Easter or Ishtar festival and not the rule for the biblical Passover.

  Link
  Christian denominations that denounce Easter as pagan, believe that Passover was the period during which Jesus ascended to the Biblical Heaven (and thus not of his resurrection). From the same Link:

  Easter, on the other, hand was confined to a Friday crucifixion and Sunday resurrection in direct contradiction of Scripture. Originally, it was on fixed dates in the cult of Attis. The word Easter was even inserted in the English KJV translation of the Bible to replace the word for Passover to further disguise the issue.

  Link

Christmas

As mentioned earlier, the Roman God Mithras' birthday had always been celebrated on 25 December. The grotto of the Vatican had been his main temple in Rome, before the Christians took it away. Similarly, many other pre-Christian Gods shared the same birthday of 25 December.

4th century Bishop [and Saint] John Chrysostom writes:
"On this day also the Birthday of Christ was lately fixed at Rome in order that while the heathen were busy with their profane ceremonies, the Christians might perform their sacred rites undisturbed. They call this the Birthday of the Invincible One; but who is so invincible as the Lord? They call it the Birthday of the Solar Disk, but Christ is the Sun of Righteousness."

Link
The "Invincible One" that Chrysostom referred to was the deity Sol Invictus Mithras - Invincible Sun Mithra, and his Birthday was called Natalis Solis Invicti (see Dominus and Natali).

The birth of Christ was assigned the date of the winter solstice (December 25 in the Julian calendar, January 6 in the Egyptian), because on this day, as the Sun began its return to northern skies, the pagan devotees of Mithras celebrated the Dies Natalis Solis Invicti (Birthday of the Invincible Sun). On December 25, 274, [Roman Emperor] Aurelian had proclaimed the Sun God the principal patron of the Empire and dedicated a temple to Him in the Campus Martius. Christmas originated at a time when the cult of the Sun was particularly strong at Rome.
-- New Catholic Encyclopaedia (Vol. III, p.656, 1967 ed.)

The very important 7 day Roman festival of Saturnalia, held from the 17th to 24th December, was in honour of Saturn, their vegetation God. It was followed by the equally important celebration of Mithra's birth on the 25th.
In the northern countries of Scandinavia, Germany and England the pre-Christian people celebrated the midwinter festival of Yule to mark the winter-solstice.

According to The Origins of Christmas and Easter article from the Christian Churches of God site:

The gospels say nothing as to the day of Christ’s birth and the early Church did not celebrate it.
The custom of celebrating Christ’s birth began in Egypt, being derived from the Mother goddess cult there, and the Christians there celebrated it on 6 January. By the fourth century it had become generally established in the East (Frazer, v, p. 304). The western church had never recognised 6 January as the true date and, in time, its decision was accepted by the eastern church. At Antioch this change was not introduced until about 375 CE (Frazer, ibid.).
The origin of the practice is plainly recorded by the Syrian Christians as we see from Frazer quoting also Credner and Momsen and also Usener (v, pp. 304-305).

The reason why the fathers transferred the celebration of the sixth of January to the twenty fifth of December was this. It was a custom of the heathen to celebrate on the same twenty-fifth of December the birthday of the Sun, at which they kindled lights in token of festivity. In these solemnities and festivities the Christians also took part. Accordingly when the doctors of the Church perceived that the Christians had a leaning to this festival, they took counsel and resolved that the true Nativity should be solemnized on that day and the festival of the Epiphany on the sixth of January. Accordingly, along with this custom, the practice has prevailed of kindling fires till the sixth.

...
Frazer says:

Thus it appears that the Christian Church chose to celebrate the birthday of its Founder on the twenty-fifth of December in order to transfer the devotion of the heathen from the Sun to him who was called the Sun of Righteousness (p. 305).

Once again, it's apparent that 25 December was adopted because the Romans and others in the west were still attached to Mithras' birth celebration and needed to be weaned off from their solar God.

See more:
Where is the Christ in Christmas?

New Year's

The Romans, after the adoption of the Julian calendar, kept the 1st of January as a general holiday. Sacrifices were made to Janus; gifts and visits were exchanged, and masquerading and feasting were general...

Participation in the ordinary New Year's Day observation as well as in the Saturnalia of December was from the first discouraged by the Church.

When about the 5th century the 25th of December had become a fixed festival commemorative of the Nativity, the 1st of January assumed a specially sacred character as the octave of Christmas Day and as the anniversary of the Circumcision."
-- Encyclopedia Britannica, 11th edition, 1911

Janus was of course the two-faced Roman God who gave rise to the name of our first month of January.

The Epiphany and the Three Kings

As seen under Christmas above, the early Church decided to make the 6th of January into the Epiphany. Why? Why else but to replace a pre-Christian festival relating to the real Epiphany.
Dionysus, the Greek God of the Vine and merrymaking, was also known for his miracle of changing rivers, streams and other waters into wine. In pre-Christian times, his religion was spread around the Mediterranean - from Thrace, all over Greece including Anatolia, to Egypt and the Middle East.
Epiphany is celebrated by some Christian denominations today on January 6.

The date the Church celebrates the feast of the miracle of Cana [where Jesus turns water into wine] is 6 January, the feast of the Epiphany. Epiphania means "appearance" in Greek and refers to the revelation of the Lord's power. In pagan antiquity 6 January was the day celebrating the revelation of a different divine power and wine miracles performed by a different god: It was the feast of Dionysus, the Greek god of wine. In fact the motif of the story, the transformation of water into wine, is a typical motif of the Dionysus legend, in which this miracle serves to highlight the god's epiphany. And hence it is timed to coincide with the date of the feast of Dionysus, from January 5th to 6th.

The 6th of January became for Christians the feast of the power revelation (epiphany) of their God, thereby displacing the feast of Dionysus's epiphany. As Bultmann says,

"No doubt the story [of the marriage feast at Cana] has been borrowed from pagan legends and transferred to Jesus".

In Christianity,

The observance [of Epiphany] originated in the Eastern church, and at first celebrated the total revelation of God in Christ. Later it focused upon two events of Jesus' ministry, his baptism (Mark 1:9-11) and the changing of the water into wine at Cana of Galilee (John 2:1-12).
...When the observance of January 6 spread to the West, it became associated with the visit of the Magi to the infant Jesus (Matthew 2:1-12), an event that in the West originally formed part of the Christmas observance (Grollier).

Link
Today, the Armenian Church continues to hold Christmas on the 6th of January.

So the western Churches have turned the 6th of January into the day for commemorating the three Magi (not Kings, nor merely "wise men") visiting baby Jesus, which the west previously observed on the 25th December. Yet the Magi, who were Zoroastrian priests, are not part of the Christian tale either:

the story of the Magi, who were said to have visited the newborn Jesus, resembles an earlier story of Magi who looked for a star foretelling the birth of a Savior, in this case Mithras. Magi were not kings but Zoroastrian astrologers...

From: Zoroastrianism: The Forgotten Source
Far from being some coincidental resemblance, the inclusion of the three Magi in the Nativity story was merely another Christian appropriation of the much older tale of Mithras. It was also meant to trump - or appeal to - the Persians (the Zoroastrians), whose very priests Christians were willing to write into the Nativity tale:

[Picture] The Magi attend the birth of Jesus. Their "Adoration" symbolizes the submission of Mithraism to triumphant Christianity.

Link

Lent

The season of Lent (originally the word meant Spring) which is 40 days of fasting in preparation for Easter is of pre-Christian origin as well:

"It ought to be known that the observance of Lent did not exist, as long as the primitive church retained its perfection unbroken."
-- Cassianus, 5th century, referring to Lent

The 40 days of fasting during Lent was observed by the followers of the Babylonian deity Astarte, the Egyptians who worshipped Osiris, and the Yazidis (Kurdish people who profess their old religion) and in the Greco-Roman religions, like that of Mithras:

"Lent ... Observance of Lent [by Christians] is as old as the 4th century.... The Christian observance of Lent may have a parallel in the fasting practiced in Greco-Roman mystery religions."
-- The Columbia Encyclopedia (2001)

Thus in pre-Christian Rome:

From December 25 until the Spring Equinox (Estra or Easter) were the "40 days" which later became 'Christian' Lent.

Link

St. Valentine's Day

The Columbia Encyclopedia (2001) states that this Western European "Christian" holiday is:
...originally the Roman feast of Lupercalia...[which is an] ancient Roman festival held annually on Feb. 15th."

In pre-Christian Rome, people celebrated "Valentine's day" as Lupercalia, a Roman holiday that took place during the ides of February (the 15th). They believed that the goddess Juno Februata (where the name February comes from) inflicted her "love fever" on the young and unwary.

...For years the Christian church tried to suppress the festival of Lupercalia. Interestingly, the Church did not object to the festival for its love celebrations but for the pagan beliefs that rejected the Christian god. In 496 C.E., Pope Gelasius changed Lupercalia from the 15th to the 14th and renamed it after the legendary St. Valentine in an attempt to stop the pagan celebration.

...To this day, men and women send love notes to each other. And in elementary schools across the country, children still put concealed notes or gifts in a box much as the ancient Romans did.

Link
Gelasius' attempts to stop Lupercalia have obviously failed, as we continue the pre-Christian Roman tradition to this day.

Sunday

Sunday was not made the "official" Sabbath day until c364 CE, when

The Church Council of Laodicea ordered that religious observances were to be conducted on Sunday, not Saturday. Sunday became the new Sabbath.

Link

Saturday is the Biblical Sabbath as per the Old Testament and its followers in Judaism. However, since much of Roman Christianity was itself derived from Rome's earlier religion of Mithraism which had the solar deity Mithra at its centre, Sunday which had been the sacred day (called the Lord's Day) of Mithras was retained as holy in Christianity:

Sunday was sacred and known as "the Lord's Day" centuries before Jesus was ever born. [Link ]

In competing with the pre-Christian religion of Mithraism, the early Church yet again appropriated the ever-popular pagan observance of Sunday as the special day of the week.

Though they were willing to take over the same day as the followers of Mithras, the early Church fathers made it a point to choose a day separate from the one Jews observed in order to keep themselves distinct. Much after the fact, they reasoned that the choice of Sunday was because Jesus' Resurrection was supposed to have happened on this day. It is still the reason given by those denominations that have grown accustomed to keeping Sunday, as opposed to Saturday, holy.
Yet, the same is also true of Mithra:

Like the Christians, they [the Mithraists] celebrated the atoning death of a savior who was resurrected on a Sunday.

Logos

the doctrine of the logos ("the Word") came from the Stoic philosophers

Link
The concept of Logos, literally 'word' in Greek, originates from pre-Christian Hellenic thought. In Platonic philosophy, it referred to the means by which the transcendent God (who, being transcendent, cannot have contact with the material world), takes on the intermediary form of Logos to reveal himself to humanity. The term "Logos" as Word of God, came to be applied to several pre-Christian deities and Godmen in the Mediterranean region. Later, Christianity took this concept and made Jesus out to be the Logos, the Word of God.
The pagan Romans referred to the Roman God Mercury as Logos, as even the early Christian apologist St. Justin Martin had to admit in his First Apology:

Mercury is the angelic word [Logos] of God

In Forgery in Christianity, Joseph Wheless refers to the Catholic Encyclopaedia and early Church father Lactantius, to show how eventually

the old Greek "Logos" of Heraclitus and the Philosophers [was] revamped by the Greek priest who wrote the first chapter of the "Gospel according to St. John"
...
The inspired "revelation" of the Holy Ghost concerning the holy Pagan doctrine of the "Creative, Logos" or "Word of God," made flesh in Jesus Christ, is thus "taken and molded to his dogma" by the Holy Saint John:

"In the beginning was the Logos, and the Logos was with God, and the Logos was God. The same was in the beginning with God. All things were made by him [i.e. by the Logos); and without him was not anything made that was made." (John, i, 1-3.)

The doctrine of the Logos was a Pagan speculation or invention of the Greek philosopher Heraclitus, who lived 535-475 Before Christ, and had never heard of Christ. From it the science of Logic takes its name; and on it the first principle of Stoicism and the Christian doctrine of "The Word" are based. If this startling statement out of secular history is questioned, let CE [Catholic Encyclopaedia] bear its clerical witness to the Pagan origin of the Logos and the curious Christian metamorphosis of it wrought by "St. John" and the Church Fathers:

"The word Logos (Gr. Logos; Lat. Verbum) is the term by which Christian theology in the Greek language designates the Word of God, the Second Person of the Blessed Trinity. Before St. John had consecrated this term by adopting it, the Greeks and the Jews had used it to express religious conceptions which, under divers titles, have exercised a certain influence on Christian theology. ... It was in Heraclitus that the theory of the Logos appears for the first time..." (CE. ix, 328-9.)

-- Forgery in Christianity, by Joseph Wheless

Christos and Chrestos

In the Synoptic Sayings Source [Q source], "Christological titles for Jesus are strikingly absent [scholar-speak for 'Jesus is never called Christ']"
-- Helmut Koester, Introduction to the New Testament, vol 2, History and Literature of Early Christianity

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It is general knowledge that the Greek term Christos (Anointed One), translation of Hebrew Messiah, was used to refer to many leaders of Jewish sects before it was applied to Jesus. Chrestus was a pagan term used to refer to various pre-Christian deities.

The most ancient dated Christian inscription (Oct. 1, 318 A.D.) runs "The Lord and Saviour Jesus the Good"— Chrestos, not Christos. This was the legend over the door of a Marcionite Church, and the Marcionites were Anti-Jewish Gnostics, and did not confound their Chrestos with the Jewish Christos (Messiah).

But even so we are confronted with the difficulty that according to the received tradition the Christian Christ was never at Rome, and did not survive to the reign of Claudius. Moreover, if it be argued that Suetonius does not employ the phrase "impulsore Chresto" literally, but intended it to carry a metaphorical meaning, even so we have to remember that Christos does not necessarily refer to Jesus. Christos is simply the Greek for the Hebrew Messiah , the "anointed," and at this period there were many claiming to be this "anointed." The reference may then be simply to a Messianic riot of some sort among the Jews.
-- Did Jesus Live 100 B.C.? by G. R. S. Mead

An offshoot of Gnosticism was Gnostic Christianity, one of the early Christian sects. The Gnostic Christians were later deemed heretical by the mainstream Christian Church and persecuted to extinction. The Marcionites mentioned above were Christian Gnostics (not the non-Christian or pre-Christian kind of Gnostics).

The Greeks used both the word Messias (a transliteration) and Christos (a translation) for the Hebrew Mashiach (Anointed). The word Christos was far more acceptable to the pagans who were worshiping Chreston and Chrestos.
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According to Realencyclopaedie, the inscription Chrestos is to be seen on a Mithras relief in the Vatican. According to Christianity and Mythology, Osiris, the Sun-deity of Egypt, was reverenced as Chrestos. In the Synagogue of the Marcionites on Mount Hermon, built in the third century A.D., the Messiah's title is spelled Chrestos. According to Tertullian and Lactantius, the common people usually called Christ Chrestos.

From: Words with Heathen Origins in the Scriptures

Early Christian writers almost uniformly spelled the name of Christ, not "Christos" (the Anointed), but "Chrestos." Chrestos was a Pagan name given to the judge of Hades or the lower world.
-- The Christ, John E. Remsberg

Hades was the underworld of pre-Christian Greek beliefs.

Dominus and Natali

The Latin term Dominus ("Lord") is still generally, and wrongly, believed to refer to Christ. However, Romans had always used Dominus to refer to the pre-Christian Roman God Mithras. Sol Invictus (Mithras) which is Latin for "Invincible Sun Mithra", was the name Romans gave to the same God that Persians called Mithra. Romans often called him Dominus or Sol Dominus Invictus (the Lord, the Invincible Sun). Originally 'Dominus' was uniquely a pagan reference to deity, though it has a generic meaning as Lord. It was initially considered as specifically pagan Roman as it is now regarded as a uniquely Christian term. It was adopted along with many other Roman and Mithraic beliefs, festivals and rituals.

Similarly, many Christians are under the false impression that the Latin word Natali (and thus its subsequent presence in names like Nathalie) are Christian in origin. It means "birthday", and in the Christian world this has been equated with "Christmas".
Yet before Christianity took over in Rome, Natali referred specifically to Mithras' birthday, which had always been on 25 December and was celebrated by the Mithraic priests in the Mithraeum of the Vatican. Natalis Solis Invicti ("the Birthday the Invincible Sun") and Dies Natalis Dei Solis Invicti ("The Birthday of the Invincible Sun God") referred to the birthday of Deus Sol Invictus, in other words: Mithras.