Among the Greek goddesses and Assyrian altars of the British Museum can be heard the growing rumble of the imminent Apocalypse. At least, that’s what the Jehovah’s Witnesses who gather there every Saturday tell me. Even if I’m a bit deaf to it, they’re not – and they’re using the Museum to prove it.

These Witnesses are going on Bible tours, where they are taken around the museum to see objects relating to history and prophecies as given in Scripture. They are turns round the Classical world with an Apocalyptic twist. With a variety of routes and subjects, hundreds of people – not exclusively Witnesses – turn up each week.

Many of them come from abroad, some especially to go on the tours. One such woman, from Zimbabwe, segues smoothly and without irony from talking about Harare’s terrible problems to cheerfully predicting the end of the world. If the Bible’s prophecies are right – and they are, she says – “The good times are here!” Never before has Armageddon sounded so cheery.

The tourists I meet take pains to stress that their faith is not in stones but in Scripture, a sentiment seemingly at odds with the tours’ purpose: who needs physical proof for a fundamental belief? Nor do any of them see the tours as a Da Vinci Code backlash – although the setting and the methods summon up the comparison. All that’s really missing is the ominous music and an albino monk.

Emmanuel Zervides is the charismatic, learned showman at the centre of the tours. A Greek forced out of Egypt after Nasser’s expulsion of nonnationals, he moved to London and started taking tours in 1970. Since then, they have expanded into a non-profit-making venture with a dozen volunteer guides. All tourists are asked to donate 50p to the Museum. According to Zervides, the tours have raised £150,000 for the British Museum since 1989.

He cuts quite a dash as he takes the first tour – a greying Barnum presiding over stone lions. He darts between objects as he keeps us in suspense about the significance of the 13 Israelites on the Black Obelisk of Shalmaneser III (they stand for each tribe of Israel) and wildly waves his hands while explaining the deficiencies of Assyrian sculpture (all too flat and lifeless). The showmanship is tremendously entertaining and does nothing to detract from his lucid history lesson, which uses the museum’s artefacts as evidence to be questioned and eventually reconciled with the Bible. It resembles a vivid university tutorial, given by a teacher with a flair for amateur dramatics; Zervides pause pointedly before stage-whispering his thesis: “Don’t you see? The stones are crying out!”

Zervides’s showmanship would have helped Gary Hollington, another guide, who led the second tour – it would at least have distracted from the flaws in his argument. The tour, called “This is history written in advance”, purported to tie down prophecies in the Book of Daniel to Greek and Roman items fabricated centuries afterwards, such as busts of the early Roman Emperors and coins struck by Alexander the Great. Unfortunately Hollington neglected to mention the dispute over the date of Daniel; prophecies work much better when they predate the events they foretell. But if these were prophecies and they are true, the Witnesses hold, then all the others in Scripture – including the rapid approach of the Apocalypse, as calculated and then recalculated by the Witnesses – must be true.

What starts out, however, as a whistle-stop plunge through Classical history ends up as a lesson in dubious hermeneutics. Take Daniel xi, 5, cited as a proven prophecy: “Then the King of the South shall grow strong, but one of his officers shall grow stronger than he and shall rule a realm greater than his own realm.” The first half is said to relate to Ptolemy, one of Alexander’s heirs, who indeed grew strong. Yet the second half of the sentence, which contradicts historical reality because no officer did grow stronger than this heir, is apparently a separate prophecy. It’s a buffet approach to the Bible, picking what suits regardless of order or logic.

I got scowls from my fellow tourists for asking about this, and Hollington, who earlier said that Daniel specifically predicted Alexander would have four heirs, none of whom were his children, told me that Daniel couldn’t know all the details of future history. Another of my suggestions, that one of Hollington’s interpretations might be a bit tenuous and ignore actual history, was greeted with a rab-bit-in-the-headlights look as he stood beside a bust of the Emperor Titus. When discussing my queries afterwards, Zervides reached for the excuses: “I studied the Bible but I can’t remember all of it”; “I can get back to you with an explanation of that”. Gary contributed his own: “I don’t claim to know every bit of the Bible.” Not even the second half of a verse you were just explaining? No.

These tours are decent introductions to Classical history led by experienced guides. But as soon as there is talk of prophecies or Scripture – and challenges to interpretations – it becomes nothing more than a Bible-versus-reason debate: as Zervides says, “You still need faith to understand it.”

In the British Museum, the glorious product of the Enlightenment, this is a profoundly disturbing sentiment. And still the Apocalypse rumbles away, as imminent as ever.

Meander British Museum tours: www.meander.co.uk; 020-8561 4699

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