Deception and falsification

The seventh century, the most ignorant and one of the grossest of all, has supplied more than eight hundred saints to the Roman calendar!
-- The Story Of Religious Controversy, by historian and former Franciscan monk Joseph McCabe

Though that seems like a vast number for one century, considering the number beatified and sainted during the last papacy:

Pope John Paul II has beatified 805 people and canonized a record number of saints - 280 - during his papacy.

From: Saint Mania, though he's bestowed the honour on war criminals like Stepinac and frauds like Mother Teresa.
Not all of the 805 were alive in the 20th century, but those beatified are now well on their way to eventual sainthood.

False relics of old saints and Jesus

In the past, the Church was (in)famous for swindling many rich aristocrats into buying junk - sometimes the remains of unfortunate unknowns - which buyers were told were relics of saints.

Thousands of believers were deceived into purchasing expensive relics from [Pope] Gregory I, who claimed they belonged to saints – many of whom never existed!

Link
For instance, 40 non-existent saints were removed from veneration by Pope Paul VI in 1969, such as Christopher, Valentine, Anastasia and Barbara. See: The Incredible Book of Vatican Facts and Papal Curiosities: A Treasury of Trivia by Nino Lo Bello.

In order to withstand obvious doubts about replicated relics (multiple heads of John the Baptist, for example) the Church espoused the wondrous truth that 'self-replication' was further evidence of a relic's miraculous qualities.

Link

Duplicated relics within the Vatican:

Down in the basement of the Vatican... beneath the high altar of St. Peter’s Basilica ... boxes filled with old bones, some of which are claimed to be the mortal remains of St. Peter himself.
Ten of the bones thus carefully preserved at this most holy focal point in all of Christendom, however, are the remains of domestic animals — goats, sheep, cows, swine, and a chicken. ...The bones have been certified to be the veritable remains of the Prince of Apostles himself, St. Peter. ...Most precious among the relics remaining of Peter’s skeleton in the Vatican are 29 fragments of one of his skulls. (St. Peter’s other skull is preserved in a reliquary at the Cathedral of St. John Lateran.)

The skeleton and skulls now venerated as the remains of St. Peter are not the only relics of the Prince of Apostles to have been discovered by the Roman Church, however. [More] bones were kept for fourteen years by Pope Pius XII himself, in his private apartment... the ones found in what Pius had certified to be the genuine tomb of St. Peter.
Venerando Correnti, an anthropologist hired by the Vatican in 1956 to study the pope’s prized bones ... discovered five tibias to supplement the three fibulas. This meant that he was dealing with five to eight legs!

In addition to the human remains, Correnti’s collaborator Luigi Cardini identified bones that once galumphed around as hogs, sheep, and goats — and some that scratched around as chickens. Unlike the bones said to have been found inside the graffiti-covered wall, the bones actually taken from the "true tomb of the Prince of Apostles" are not venerated. Quietly, they have been stored away in some secret location.

From: Of Bones and Boners: Saint Peter at the Vatican
See also: The Legend of Saint Peter: A Contribution to the Mythology of Christianity, a summary of Arthur Drews' Die Petruslegende "The Peter Legend".
And Making a Saint out of Peter

Some of the Virgin Mary's hair and milk were exhibited at Laon, Soissons, and a milk tooth of child Jesus was kept at Soissons. How authentic were these?

• There seems to have been enough milk of the Virgin -- some of it was still exhibited in Spanish churches in the nineteenth century -- preserved in Europe to feed a few calves.
• There was hair enough to make a mattress.
• There were sufficient pieces of "the true cross" to make a boat [as Protestant reformer Calvin had remarked].
• There were teeth of Christ enough to outfit a dentist (one monastery, at Charroux, had the complete set.)
• There were so many sets of baby-linen of the infant Jesus, in Italy, France and Spain, that one could have opened a shop with them.
• One of the greatest churches in Rome had Christ's manger-cradle.
• Seven churches had his authentic umbilical cord, and a number of churches had his foreskin (removed at circumcision and kept as a souvenir by Mary).
• One church had the miraculous imprint of his little bottom on a stone on which he had sat.
• Mary herself had left enough wedding rings, shoes, stockings, shirts, girdles, etc., to fill a museum. You can, if you are good, see one of her shifts still in Chartres cathedral; though in this coarser age of ours it is called a "veil."
• One church had Aaron's rod.
• Six churches had the six heads cut off John the Baptist ...

Every one of these things was, remember, in its origin, a cynical, blasphemous swindle; and Rome was the great trading center. All the wriggling of all the G.K. Chestertons and all the Jesuits and Paulists in America will not obscure that. Each of those objects was at first launched upon the world with deliberate mendacity. Honor and honesty were as rare as chastity in Christianized Europe and as rare in the Church as in the "world." To talk of those ages as "spiritual" and ours as "materialistic" ... One is almost disposed to ask for an application to the clergy of the law about obtaining money under false pretenses.
-- The Story Of Religious Controversy, by Joseph McCabe

• Fragments of 'the true cross', pieces of saints' bodies, still-wet tears shed by Jesus, barbs from the Crown of Thorns, Mary's undergarments - such were treasured in jewelled cases in every major church.
• A ruler of Saxony proudly possessed 17,000 relics, including a branch from Moses' burning bush and a feather from the wings of the Angel Gabriel.
• Canterbury Cathedral displayed part of the clay left over after God fashioned Adam.
• Historian Charles Mackay said Spanish churches had six or seven thighbones of the Virgin Mary, and others had enough of St Peter's toenails to fill a sack.
• Voltaire noted that six sacred foreskins were snipped from Jesus at his circumcision; later researchers counted fifteen

-- Holy Horrors: An Illustrated History of Religious Murder and Madness, by James A. Haught

The names of the three Wise Men assigned by legend -- Gaspar ("white"), Melchior ("light"), and Balthasar ("the lord of the treasury") -- are as unhistorical as the report that their skulls were discovered by Queen Helena, mother of Constantine the Great, taken to Constantinople, and thence to Cologne, whose cathedral has for centuries claimed them to be deposited in its Chapel of the Three Wise Men.
-- Harper's Bible Dictionary

A number of further forgeries (Donation of Constantine, etc.) established the Pope's royal dignity, and a vast number of falsified or forged decrees of Councils proved his spiritual supremacy. There had been, on the admission of all historians, six hundred years of forgeries.
-- The Story Of Religious Controversy, by Joseph McCabe

The Donation of Constantine

the document showed that the Roman Church was, from the days of Constantine, pronounced as the supreme church, had a right to the regions around Rome and was superior to the emperor.

Believing the document shown to him by Pope Stephen III to be true, the king of the Franks:

Upon defeating the Lombards, he duly handed to Stephen the regions mentioned in the Donation. This was how the papal states came into being.

The document was finally shown to be a fraud in the fifteenth century by the Italian humanist, Lorenzo Valla (c1406-57).
...While Valla's argument convinced the impartial scholars, Rome continued to deny for many centuries that the Donation was a fraud. Thus one of the most significant triumph in the history of the Roman Church was achieved by fraud.

Link, the section The Use of Forgery to Enforce Claims of Papal Supremacy
Since the Donation of Constantine was a forgery, the 12th century English Pope Adrian IV really didn't own Ireland and therefore had no right to give it to England. [Link]

The Isidorian Decretals

...perhaps the most important forgery in the steps towards papal supremacy. The documents were supposedly collected by St. Isidore of Seville (d.636) ... supposed to prove that from the earliest days the Church of Rome had the right to issue laws, validate council decisions and depose bishops. These documents are known today to be forgeries. They were actually deceitfully composed by the Frankish Court around the year 850.

They first appeared when 9th century Pope Nicholas I clashed with the archbishop Hincmar of Rheims

on the issue of the right of the Roman church to depose and install bishops. Nicholas I ...cited the Decretals, claiming to have ancient copies of them. It was obvious that Nicholas lied, for the forgery was only less than two decades old then!

11th century Pope Gregory VII used the Decretals to claim the right to depose princes, kings and emperors. And his successors continued to do likewise.

Gregory not only used fake documents, he had a whole school set up to manufacture still more fraudulent documents

Link, the section The Use of Forgery to Enforce Claims of Papal Supremacy

That the Church was used to fabricating "pious" lies and creating forgeries is a well-known fact, see Would they lie? – Copy and Glorify!

Of course, the worship/veneration of relics has all but ceased, it was only the mass creation and selling off of them that had halted for a while.

However, peddling relics and other allegedly "historic" artefacts no longer seems to be confined to the past. Indeed, it seems to have made a major comeback. Unfortunately for the forgers who appear to have little understanding of today's scientific methods, it's easy to determine the truthfulness of their claims.
That the medieval forgery The Shroud of Turin is a fake isn't in doubt by real scientists (though recently some supposedly "unbiased" pseudo-scientist claimed it had been re-examined by carbon-dating yet again to find it "authentic", but scientists have once again shown these claims to be false).

Recent pious frauds who've tried to pass of fake items as Christian relics have been made infamous:

• The "James Ossuary": this was the box purported to contain the bones of one "James son of Joseph, brother of Jesus" as per its inscription (which actually states "Jacob son of Joseph, brother of Joshua" and with the second half mis-spelled). The second half of the inscription is a later forgery. The ossuary is unreliable as any kind of evidence for Jesus Christ.
  Ossuary was genuine, inscription was faked, by Rochelle I. Altman, 2002

  As an expert on scripts and an historian of writing systems, I was asked to examine this inscription and make a report. I did.
  The bone-box is original; the first inscription, which is in Aramaic, "Jacob son of Joseph," is authentic. The second half of the inscription, "brother of Jesus," is a poorly executed fake and a later addition. This report has already been distributed on at least two scholarly lists.
  ...
  The person who wrote the second part ... may have been literate, but it is doubtful that he was literate in Aramaic or Hebrew. ... There is nothing logical about these misspellings. They smell of someone guessing how the words "brother of" and the name "Joshua" would have been spelled a couple, three hundred years earlier. ... Part 2 has the characteristics of a later addition by someone attempting to imitate an unfamiliar script and write in an unfamiliar language.

  See also: The "James Ossuary" – A Box of Tricks and Proof of the Historical Jesus, or Rush to Judgment? - Frank Zindler
• Forgers 'tried to rewrite biblical history' - The Guardian, December 31, 2004

  "Hundreds of biblical artefacts in museums all over the world could be fakes, it has emerged after Israeli investigators uncovered what they claim is a sophisticated forgery ring."

With such a long tradition of passing fakes off as "authentic relics", it is hardly surprising that pious Christians today would still be trying to forge "proofs" for the validity of the faith.

And a very old Orthodox 'miracle' exposed as a fraud:

The 'Holy' Light of Jerusalem

Alleged fulfillment of Messianic Prophecy

The Fabulous Prophecies of the Messiah:

Every case of alleged fulfillment of messianic prophecy suffers from one of the following failings:
(1) the alleged Old Testament prophecy is not a messianic prophecy or not a prophecy at all,
(2) the prophecy has not been fulfilled by Jesus, or
(3) the prophecy is so vague as to be unconvincing in its application to Jesus.

That the so-called Messianic prophecies of the Jewish Scriptures were the immediate source of the Christ is apparent. That he was, however, merely a borrowed idea and not a historical realization of these prophecies is equally apparent. The Jews were expecting a Messiah. Had Jesus realized these expectations they would have accepted him. But he did not realize them. These prophecies were not fulfilled in him. He was not a son of David; he did not deliver his race from bondage; he did not become a king, the important events that were to attend and follow Messiah's advent form no part even of his alleged history. His rejection by the Jews proves him to be either a false Messiah, or an imaginary being - a historical myth or a pure myth - in either case a myth.

The Jewish argument against Jesus as the Messiah is unanswerable. ...
-- The Christ, John E. Remsberg

"A virgin shall be with child"

Perhaps the best known but most misunderstood OT proof-text claimed to be a prediction of Jesus and his virgin birth is the passage in Isaiah, Chapter 7, verse 14. According to Matt. 1:23, Isaiah is supposed to have said, "Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel." But when we turn to the Hebrew text of Isaiah 7:14, we find a somewhat different reading:

Behold, the young girl [no specification of virginity] is with child, and will give birth to a son, and she will call his name Emmanuel. [my translation]

The differences are striking. Whereas Matthew has the term "virgin," meaning a woman who has never had sexual intercourse, the Hebrew has the word alma -- a word which simply means a young woman. Hebrew has a word for virgin -- bethulah -- and Isaiah would certainly have used it if "virgin" is what he meant. But far more important than the difference in the type of woman involved is the verb in the sentence. Matthew reads Isaiah with a future verb, as though Isaiah is predicting the distant future. But Isaiah tells us the young girl is already pregnant. If Jesus is the babe in question, this is the longest pregnancy in history, and the really miraculous part of the nativity story has been overlooked for nearly two millennia!

We may note a disagreement also as to just who it is that will do the Emmanuel-calling: In Matthew we read "they will call his name Emmanuel," as though it is something that undefined people in the future will do. But in Isaiah the Hebrew reads "she will call" -- meaning the mother of the child. Since Mary did not name her baby Emmanuel, we see how irrelevant this prophecy is to the case of Jesus. Moreover, no one in the NT ever refers to Jesus as "Emmanuel." The only occurrence of the word in the entire NT is right here, in this misquotation from Isaiah. Finally, we may note that Isaiah's prophecy is aimed at King Ahaz, who is told that before the child Emmanuel grows up, "desolation will come upon the land before whose two kings you cower now." [New English Bible (NEB)]

From: A Nativity Potpourri

See also:

• The myth of the "prophetic virgin birth": Though the mistranslation of the Old Testament's young woman into virgin in the Greek Septuagint had been pointed out, St. Jerome of the 4th century consciously persisted in re-introducing this error in his Hebrew-to-Latin translation of the same. More here.
• Prophecies: Imaginary and unfulfilled
• The Problem of the Virgin Birth Prophecy
• A Nativity Potpourri - the section Bethlehem And The Roman Census explains how

  biographies of Jesus came to be fabricated in which the would-be savior was born in Bethlehem.

• The section Neither Zoroastrian Saoshyant nor Judaic Messiah is about how Christianity confused, perhaps on purpose, the Judaic concept of Messiah with the Zoroastrian concept of world-saviour Saoshyant. Christianity got the Persian tradition of the Saoshyant all wrong, and Christ failed the expectations of the Jewish Messiah.
• False Messiah