This may be the popular influence of 20th century liberalism and postmodernism (just another form of ancient skepticism) which would trade the historical method and the primary evidence for poor late-dated gnostic sources and sociological reconstructions (which have little data to go on). And sadly, sometimes people just believe that the Da Vinci code was non-fiction, and that the church was in cahoots in the 3rd century.
In fact, the historicity of the New Testament is astounding. If you wanted to take seriously the claims of Jesus, you couldn't ask for better. Here are a few examples off the top of my head:
1. Primary sources dated as close as 22-25 years and as late as 70 years after the event of Jesus' death and resurrection.
2. Thousands of transcribed copies in several ancient languages, from different locations and periods.
3. Many manuscript fragments with early dates, e.g. the earliest, the John fragment (Papyrus P52) at the John Rylands Library in Manchester in England, dates from as early as 125 AD.
4. Multiple independent accounts of eye witness testimony including hostile sources.
5. Biographical accounts written as history.
6. The evidence and weight of the incidental accounts, the New Testament letters, which contain numerous historical details, facts, references and mutual understanding, taken for granted and mentioned in passing.
7. The disciples are frequently portrayed in a negative light in the gospels.
8. The testimony of women is relied on at various key points in the gospels, something which a 1st century fraud would not likely have included.
9. Integrity of the eye witnesses under intense pressure and scrutiny and brutal persecution. Most of the original apostles died horrific deaths, refusing to recant what they saw and heard (1 John 1). In contrast, the Watergate scandal lasted all of a few days before the group fell apart.
10. Many accurate geographical and political references, often of a very technical nature (e.g. various political offices and ranks, shipping navigation, climates, architecture).
In summary, Christianity is an historical claim about an historical person, Jesus of Nazareth. Anyone is free to investigate these claims for themselves, according to the historical method.
For more on this, read Paul Barnett's "Jesus and the Logic of History" (http://www.amazon.com/Jesus-History-Studies-Biblical-Theolog...), or "New Testament Documents: Are They Reliable?" by FF Bruce (himself a Rylands Professor).
See Paul Barnett's "Jesus And The Logic Of History" for the historical method as applied to Jesus: http://www.amazon.com/Jesus-History-Studies-Biblical-Theolog...
As a result, Rovelli ventures outside his circle of competence when he views Christianity as a set of "written-down beliefs" disconnected from actual historical events.
In fact, for someone interested in ancient history, the primary and secondary sources for understanding the historical origin of Christianity tell a remarkably different story, namely that there is a very strong connection between the historical person of Christ and the people that followed him. Specifically, that these people followed him on the basis of his historical person, his death and resurrection, of which they were fully convinced, often at great personal cost.
As Paul of Tarsus said under trial, being someone who had previously physically persecuted the early Christians: "Why should any of you consider it incredible that God raises the dead?"
For Paul, it was not a question of probability or "how often does this happen every day" (which would be frequentism), but of historical happening, did it happen? He, like Thomas, would not follow the risen Christ unless he saw him himself, and this is what he (according to the sources), amongst others, claimed to have happened. So that Christians today (as with Christians then) are Christians on the basis of their understanding and acceptance of the historicity and meaning of the events concerning Christ. For Paul's own words, and a remarkable piece of ancient history, see his letter to the Corinthians, 1 Corinthians 15:3-9.
Note also that our knowledge of Christ as an actual historical person is not limited to the writings of those that followed him and were devoted to him.
For a good introduction to the historical method and its application to Christ, see Paul Barnett, historian, "Jesus and the Logic of History": http://www.amazon.com/Jesus-History-Studies-Biblical-Theolog...
That view is not compatible at least with the actual history of 1st century Christians. For them, Christianity was about the historical person of Christ. See Paul, a former persecutor of Christians, writing to Christians in Corinth, circa AD 55:
"And if Christ has not been raised, our preaching is useless and so is your faith. More than that, we are then found to be false witnesses about God, for we have testified about God that he raised Christ from the dead." - 1 Corinthians 15:14-15
Christianity is about the person of Christ, it's a historical claim, and therefore open to investigation by reason, according to the historical method. For an ancient historian's understanding of the historical method as applied to Jesus, see Paul Barnett's "Jesus and the Logic of History" (http://www.amazon.com/Jesus-History-Studies-Biblical-Theolog...)