In 706AD the caliph al-Walid decided to commission a building as a centrepiece for his new capital, Damascus. Only 74 years had passed since the death of the prophet Muhammad; the Arabs\' new empire was still in the making, and there was no such thing as imperial Islamic architecture. The caliph found inspiration for his mosque in both Christian and pagan temple architecture. And while he built it on the site of one of the greatest of all Roman temples, demolishing the Christian church that stood inside the precincts, he incorporated many of the Roman stones, as well as the tomb of John the Baptist. For decoration, he brought Byzantine craftsmen over to piece together the vast gold mosaics. The idea of borrowing is untroubling in architecture – we expect to see continuity and evolution in buildings. But the idea that religions evolve out of one another is more disturbing. Christians have choked on the notion that many of their rituals were borrowed from pagan rites. And heaven help the historian who dares to suggest that Islam might be a product of earlier religions and not, as the faithful insist, a revelation direct from God. Tom Holland has done exactly this in his brilliantly provocative new book – and we must hope that heaven is smiling on him now. Holland is the author of two extremely successful works of ancient history – successful in both the creative and the commercial senses. In Rubicon, he traced the end of the Roman Empire. In Persian Fire, he focused on the fifth-century BC conflict between the Persians and Greeks, between east and west. In the Shadow of the Sword is a more ambitious and more important book. The Roman and Persian empires are traditionally seen as collapsing into a void that our schoolbooks called the Dark Ages. Holland\'s thesis is that there was no void: depending on how you interpret the material, the decline of those empires led to the rise of the Arabs, or the rise of the Arabs led to their decline. To test this idea, Holland ranges around the centuries. Not content with bringing us the end of Rome, he mentions its foundation as well, something he also does with Judaism and the Israelites, with Jesus and Christians, with Zoroaster and the Persians. He is a restless wanderer across the ancient world, both geographically and intellectually. Abraham, Isaac and Moses have walk-on parts, as do the emperors Constantine and Valerian, the empress Helen, Saint Simeon the Stylite (both of them, for it appears there were two) and a dazzling range of other characters from late antiquity. There are so many of them – and few stay around long enough for a reader without prior knowledge to get a real grip on them – that the narrative risks being overwhelmed by the comings and goings. But Holland is a skilful and energetic narrator, and while he guides us along the more intricate twists and turns of the period, he also keeps our eyes on the bigger story – on the revolution that brought down the old order and ushered in the new. For this was the period, Holland says, when allegiance to land, tribe or state was superseded by devotion to one almighty deity. The assertion that Rome and Persia declined because of \"the revelation of the word of God to His Prophet in far-off Mecca\" is likely to be less controversial than Holland\'s examination of the details of the life of that prophet. He counters the widely accepted – and, to most Muslims, inviolable – view of Muhammad\'s life and the revelation of the Qur\'an with what he calls \"the traditions of secular scholarship\". These traditions are based on an insistence on hard evidence and a demand that such evidence be scrutinised. The problem with the life of Muhammad is that there is almost no textual support for it until almost two centuries after his death. Holland is not going so far as to say that he never existed. Just that the account we have comes from the 800s, by which time Haroun al-Rashid was caliph over an empire that stretched from China to the Atlantic, and the 1,001 Nights was being compiled. The veracity of details and perhaps also some of the more important moments of the prophet\'s life were – are – impossible to prove. The same goes for the Qur\'an. There is no written mention of it in the period immediately following Muhammad – nor any commentary on it until the eighth century. Holland does not, perhaps, give enough weight to the value of oral tradition, the route by which the Qur\'an is said to have been received (Muhammad is widely held to have been illiterate) and initially preserved. But his investigation does turn up some exciting possibilities as to the origin of the text and also to the location of Mecca: Holland points out that \"there is not a shred of backing\" in the Qur\'an for locating Mecca in the Hijaz. The first text-based claim for its location in what we now know as Mecca, written a century or so after the revelation of the Qur\'an, was a preposition \"taken wholly for granted\". He might be right, he might be wrong, but there is no denying that the challenge is both stimulating and, in a world of increasingly rigid Muslim dogma, refreshing. The Qur\'an anticipated the day of Holland\'s coming (or someone very like him). Sura 25 instructs Muslims to counter the claim that \"these are fables of the ancients which he has got someone to write down for him\" with the insistence that it was \"revealed by Him Who knows every secret\". For believers, these words are proof enough of the veracity of the Qur\'an. Some have gone further and used them as justification for intellectual, legal and physical attacks on people who claim otherwise. The lives of some people who have dared to question the historicity of the prophet Muhammad and the Qur\'an have been ruined, even ended. We must hope that Holland is spared their wrath and that his excellent book will be lauded, as it should be, for doing what the best sort of books can do – examining holy cows.