The three topics which suggest that Jesus never existed are:
History, Comparative Religion and Solar Mythology. Here we go.
1. History. It's inconceivable that during the alleged time of Jesus no one bothered to write down anything about this most extraordinary person, yet we have nothing. Even the earliest Bible reference to Jesus dates to at least A.D. 64, and the first Gospel, the Gospel of Mark, dates to at least A.D. 70 (and probably to A.D. 170).
2. Comparative Religion shows that the story of Jesus already existed in numerous religions prior to the alleged time of Jesus. Chrishna, Horus, Orpheus, Bacchus, Osiris, Dionysus, Buddha, Apollo, Hercules, Adonis, Ormuzd, Mithras, Indra, Œdipus, Quetzalcoatle, etc. The motif of a Crucified Savior was already extant prior to the alleged time of Jesus.
3. Solar Mythology shows the story of Jesus is just an allegory for the sun passing through the Zodiac and the passage of the seasons of the year. Jesus travels throughout his one year ministry, and the description of his travels exactly match that of the sun traveling through the Zodiac during the year. Here we have the origin of the Jesus story. This common origin explains why all the stories of crucified saviors are essentially the same.
HISTORY.
If Jesus actually existed and did all the miraculous things he is said to have done then surely many people would have written about it during and immediately following Jesus' life. Writing was common at the time, yet an extensive search by many scholars over centuries has turned up nothing. The very few references to Jesus that allegedly date back to his lifetime are clearly forgeries, forged no doubt hundreds of years later by people who realized this embarrassing lack of evidence needed to be rectified (see Joseph Wheless Forgery in Christianity).
Even if we ignore the evidence that they are forgeries, the very small number of these questionably authentic writings that allegedly date back to his alleged lifetime are still far too few. There should be a huge wealth of writing about this person that was written during his lifetime.
Jesus allegedly had crowds of thousands follow him around. Once he fed 5000 people with only a few loaves of bread and a couple of fish (Mark 6:39-44). Later he repeated the miracle again feeding a crowd of 4000 people (Mark 8:1-9). Jesus cured sick people miraculously and raised people from the dead. He changed water into wine at a wedding reception. He exorcised demons. He commanded 2000 pigs to rush into a lake and drown themselves, inciting the people of the nearby town and countryside, who asked him to leave. (No mention is made of what happened to the poor pig herder whose livelihood must have been ruined. Mark 5:1-20).
Wherever Jesus went a crowd gathered and wondered in amazement who this person was. Jesus was a very controversial person. Finally he got himself into so much trouble that huge crowds of Jews demanded his execution. There was a controversial trial followed by his public execution. Three days later he is seen walking around alive again. And no one wrote any of this down when it allegedly happened?
Even the earliest full account of Jesus in the Bible, the Gospel of Mark, is admitted by the Catholic Church to date to at least A.D. 70, a full 40 years after Jesus' alleged death and resurrection. (Mark makes reference to an event that happened around A.D. 70, so it could not have been written any earlier. Modern scholars now date the Gospels as being written near A.D. 170, a full 140 years after the alleged event, since no one makes any reference to a Gospel of Mark, or any other Gospel, prior to this time.)
It's inconceivable that no one at the time bothered to write down anything about the most important person in the whole of human history. Writing was common back then. People wrote letters. Historians wrote commentaries on current events. The Romans wrote and kept legal documents about trials. It's considered one of the best documented periods of history. Yet no one wrote anything about this Jesus; no one painted a portrait of this Jesus; no one drew a sketch of this Jesus; no one cast a coin depicting this Jesus; no one made a statue of this Jesus; no one makes any reference whatsoever to this Jesus. The historical evidence is overwhelming—the Jesus of the Bible never existed.
NEGATIVE EVIDENCE PRINCIPLE
When is absence of evidence, evidence of absence? In general a mere lack of evidence is not sufficient to conclude a proposition is false. We must also demonstrate:
1. All of the evidence used to support the proposition is untenable.
2. Adequate tenable evidence should exist.
3. A thorough search for this tenable evidence has been made and none has been found.
At this point I leave it to the reader to decide for him or her self whether the above three points have been satisfied or not, as every individual must ultimately decide what one chooses to believe. Any counter-argument will be an attack against one of the above three points. We can not prove that Jesus never existed, just as we can not prove that Santa Claus never existed. Quite a lot of people believe Santa Claus exists (mostly young people).
Being suspicious of "The Jesus Story is a Biography" theory frees our thinking and allows us to look in other places for the origin of the story. Indeed we will discover that the Jesus Story is not unique. We will find that the motif of a crucified savor who dies and is resurrected was common in other religions prior to the alleged time of Jesus. We will also discover that the story of Jesus' one year ministry parallels that of the Sun's annual journey through the Zodiac and the Sun's apparent death in Autumn and subsequent resurrection in Spring.
We will pursue these studies in parts 2 & 3. First let's examine what other scholars throughout history have said about the existence of Jesus.
—David W. Deley (2003)