It is time for the evangelists of unbelief to give up the nonsense that the figure at the heart of Christianity may have never even lived.

There are plenty of good arguments against the world's largest religion, but claiming Jesus never walked the roads of Galilee isn't one of them. To make such a claim is to turn what should be a world heavyweight contest into a lightweight sideshow.

Let me press the boxing analogy a little further. A story is told - and I hope it is true - of three young men who hopped on a bus in Detroit in the 1930s and tried to pick a fight with a lone man sitting at the back of the vehicle. They insulted him - he didn't respond. They turned up the heat of the insults - he said nothing. Eventually, the stranger stood up. He was bigger than they had estimated from his seated position - much bigger. He reached into his pocket, handed them his business card and walked off the bus and then on his way. As the bus drove on the young men gathered around the card to read the words: "Joe Louis. Boxer." They had just tried to pick a fight with the man who would be Heavyweight Boxing Champion of the World from 1937 to 1949.

Today's ardent Jesus-deniers remind me of a reckless gang throwing puerile insults at a gentle giant, oblivious to the fact that they are way out of their league.

The study of the historical Jesus is one of the West's most focused, rigorous and voluminous academic inquiries into an ancient figure. In the library of Macquarie University, home to the largest Ancient History Department in Australia, students will probably find as many historical tomes on Jesus of Nazareth as on Julius Caesar and Alexander the Great combined. It is a vast discipline operating on entirely secular principles of linguistic, literary and historical analysis. Recourse to theological validation, while a legitimate intellectual route in itself, never features in this literature.

When Richard Dawkins says "a serious historical case" can be made that "Jesus never lived at all," he no doubt receives applause from his followers, and perhaps even from his fellow experts in zoology, but in departments of Classics, Ancient History, New Testament, Jewish and Near Eastern Studies (the relevant disciplines) such a comment is entirely bemusing - all the more so when one discovers that Dawkins' sole example of this serious history is G.A. Wells. As is well known, Wells is a professor of German language at London University who, in any case, has publicly retracted his argument of the 1970s that Jesus was a myth. I have often wondered what Dawkins would say if I disputed biological evolution and cited a language professor as my sole authority (one that had changed his mind to boot).

It isn't just bestselling atheists like Dawkins who make this faux pas. A measured journalist like ABC Radio National's Michael Cathcart recently ventured unknowingly into the heavyweight ring and got caught out. In an otherwise excellent interview with Salman Rushdie, Cathcart remarked, "There's no doubt at all that Mohammed was a real person, whereas Jesus is a person who is at least ambiguous in the question of whether he existed or not." I say "caught out" because Cathcart promptly received a gentle correction from two of Australia's best known Roman historians, Professors Alanna Nobbs and Edwin Judge. "In our judgment," they wrote, "the second part of your statement is quite far from reality." They explained, "While historical and theological debates remain about the actions and significance of this figure, his fame as a teacher, and his crucifixion under the Roman prefect Pontius Pilate, may be described as historically certain."

Cathcart later described his on-air statement as an impromptu remark that didn't quite come out as he intended. Fair enough, but whatever he actually intended to say, such comments illustrate the gulf between popular scepticism and expert opinion. I've put out the challenge before: if anyone can find a full professor of Classics, Ancient History or New Testament in any accredited university in the world who thinks Jesus never lived, I will eat a page of my Bible, probably Matthew chapter 1. It's been a year since I first tweeted the challenge and religious critic John Safran retweeted it to his 60,000 followers. My Bible remains safe.

But what is the evidence for Jesus? As Nobbs and Judge explained to Michael Cathcart, "Very early Christian sources and several non-Christian, and even hostile, sources attest to the existence of Jesus in first-century Palestine, putting his existence beyond reasonable doubt."

The Christian writings are not revered by the secular historian, but nor are they rejected in an act of arbitrary scepticism. They are treated like any other set of human texts from the first century. Here's an important point: these sources date to within living memory of Jesus and were mostly written independently of each other, even if they were later collated in the New Testament. Paul, for example, wrote in the AD 50s and did not know the Gospel of Mark. Mark wrote a decade later and certainly did not possess the letters of Paul. Early date and independent attestation are basic rules of historical verification, whether studying a Roman emperor or a Galilean teacher.

The Tiberius provides a good example (he was the emperor when Jesus was crucified). Our best sources for Tiberius are Tacitus and Suetonius, both composed eighty or so years after the emperor's death in AD 37. The New Testament writings were composed much closer in time to their central figure. Several of its sources - Mark, Paul, Q, L and James - date to within 25 years of Jesus, and one crucial passage is dated to within a few years of the crucifixion, ruling out the suggestion that even the basic details of Jesus were part of a process of legendary accumulation.

What of the "non-Christian, and even hostile, sources" mentioned by Nobbs and Judge? These include Mara, Josephus, Tacitus and Pliny. Josephus is the most important. It is widely recognized that this first-century Jewish aristocrat's references to Jesus have been "improved" by a later Christian copyist (interpolations are common in ancient manuscripts). But virtually everyone writing on the topic today agrees that the paragraph in question cannot have been a complete Christian invention.

Jesus is described by Josephus as a mere "wise man" and "doer of strange deeds", expressions that no Christian propagandist would have employed. Those responsible for his execution are "men of the highest standing among us." It strains belief to think of a Christian penning such a thing; so too with the concluding comment that "the tribe of Christians, named after him, has still not disappeared to this day," which sounds like the author believed Christianity was on its way out. How wrong Josephus was!

Taken together, the non-Christian references "provide us with certainty" about Jesus's life and death, insists Professor Christopher Tuckett of Oxford University (certainly no friend of Christian apologetics), and "render highly implausible any far-fetched theories that even Jesus's very existence was a Christian invention." This is the consensus of non-religious experts today and no amount of sceptical huffing and puffing can change that.

There are, of course, some forceful arguments against Christian belief - the problem of miracles or alternative religions, the existence of evil and suffering, the scandal of hell, just to name a few. These require grown-up responses from thoughtful believers. These belong to the real heavyweight contest.

But the claim that Jesus was a figment of religious imagination and not a figure of first-century history is, quite frankly, amateur hour. It deserves to be as ignored in the public sphere as much as it is in historical circles.

John Dickson is a Founding Director of the Centre for Public Christianity and an Honorary Fellow of the Department of Ancient History, Macquarie University. He is the author of numerous books, including Investigating Jesus: An Historian's Quest.