The real mystery of the Sphinx: why do falsehoods drive out truth?

Exactly 200 years ago, Napoleon invaded Egypt. He took with him an Olympic-sized squad of scholars and artists that included 21 mathematicians, eight draughtsmen and 10 "men of letters". What did the men of letters do? They probably wrote cult bestsellers.

Our bookshops are bulging again with pyramid-shaped displays designed to the shift the newest wave of speculative ancient history. Fanciful theories about the Pharaohs, and the baffling monuments they built, have excited cranks and mystics for centuries. That they also intrigued America's hard-headed founding fathers (who knew about them via the Freemasons) you can tell from a glance at the symbols on any US dollar bill. And the fascination that occult Egyptology holds for publishers today has everything to do with the timeless allure of the folding stuff.

Abetted by huge serial deals with the mid-market tabloids, the Mystic Meg tendency has come back with a vengeance since 1994, when the Belgian engineer Robert Bauval published The Orion Mystery. He claimed that the ground-plan of the pyramids' site at Giza outside Cairo maps the position of the Constellation of Orion not in 2,500BC - the accepted date for the monuments - but much earlier, in 10,450BC. A year later, Graham Hancock's Fingerprints of the Gods updated the Atlantis myth with its argument that civilised survivors from the catastrophic end of the last Ice Age, 12,000 years ago, had passed their wisdom on to the cultures of the Near East and Central America.

It sold half a million copies to jumpy pre-millennial book-buyers with doomy threats - or were they promises? - of another climatic cataclysm just around the corner. (Clear your diaries for 5 May 2000). And so the stream rolls on, with Hancock and Bauval teaming up into the Morecambe and Wise of the Giza plateau and issuing their own newsletter to fans. Meanwhile, the newcomer Andrew Collins proposes that the neolithic engineers of Egypt hailed from Kurdistan (Hancock favours Antarctica) and could levitate vast blocks of granite with a lost form of sonic technology activated by trumpets. The phrase "loony tunes" springs to mind.

Surely this is all just harmless fun, a tangle of ripping yarns to keep cerebrally-challenged readers off the streets? Alas, the pyramid buffs take themselves very seriously and spin paranoid fantasies about their persecution by the academic establishment (and even - in one author's case - the CIA). So let's contest the best shot in their locker: the so- called rain-erosion of the Sphinx. Hancock employed this trump card to Jeremy Paxman in a Newsnight discussion of the Atlantis myth last month. Since Paxo let it pass without a murmur, here's a briefing for him.

Hancock, Collins and their chums believe that the Sphinx at Giza shows signs of weathering by rainfall, not by wind-blown sand. As the Nile delta has not had a wet climate since around 7,000BC, they take this as clinching proof that Egyptian culture arose many millennia before the orthodox dates, and so must have come from some remote source. For their guru, the maverick scholar John Anthony West, firm proof of rain erosion "would overthrow all accepted chronologies of the history of civilisation".

The trouble is that geologists have challenged the rain-erosion theory on all counts in the learned journals. Scientists can explain the Sphinx's weather-worn look perfectly well within the conventional time-frame. Yet the entire Fantasy Pyramid genre brandishes it as (literally) rock-solid scientific evidence of their position, the cornerstone of their empire. It is nothing of the sort.

So why don't publishers take their authors to task and insist on higher standards than these chaotic, waffling works ever supply? After all, this crackpot crew flies under the flags of the most respected houses in the land. Viking Penguin bankrolls Hancock, and Hodder funds Andrew Collins. Random House has just re-issued Robert Temple's The Sirius Mystery, which purports to connect ancient Egyptian culture with visiting aliens from the Sirius star system. Temple believes that "the pyramids and the Sphinx were probably built by the extraterrestrials themselves". This week, Macmillan launches Graham Phillips's Act of God: a bid to link the plagues of Egypt and the Exodus of the Israelites with the volcanic eruption on the Aegean island of Thera around 1,360BC. In this company, Phillips's reasoning sounds positively sane (no spaceships, no Atlanteans, no levitation), but his book still amounts to little more than a calculated leap in the dark.

It `s clear that Britain's once-reputable publishers no longer care two grains of desert sand about the truth-value of the "history" books they finance. They have sold whatever authority their imprints might once have claimed for a cargo of flyblown nonsense that late-Victorian charlatans such as Madame Blavatsky were already peddling at the close of the last century. The only rule that editors now bother to apply is caveat emptor.

In fact, they have even plunged beneath the shoulder-shrugging relativism of saying, "You pays yer money and you takes yer choice". The loony tunes now win the fat advances, the lavish promotion budgets and the first-class place on the hype express. In contrast, most works rooted in responsible research take a back seat, and a tiny cheque.

The chance to publish detailed, footnoted non-fiction is what economists would call a "positional good". If I have it, you don't. As with a seat for the World Cup Final or a Georgian rectory in Somerset, only a limited number of people can ever enjoy this privilege. Publishers today take on very little history anyway, even though maestros such as Simon Schama, Orlando Figes and Norman Davies prove that the proper stuff can still sell by the cartload. Now these rare and precious slots will often be filled with hypothetical hogwash. Every farrago of hippy-dippy irrationality on the shelves means that at least one truthful picture of the past will never find an audience.

Education, ministers insist, will make the difference between a thriving modern nation and a dumbed-down backwater. The book trade has already given its own two-fingered answer to that by putting its resources behind every superstitious New Age bandwagon that rolls along. The Government should take note of that the next time the business bleats about its sacred cultural mission and the tax-breaks it deserves.

This April, British publishers will wave their most pompous banners to celebrate World Book Day on a grand scale. Expect weeks of uplifting guff about the role of books in spreading enlightenment, especially to children. Then check out the flaky fairy-tales that pass for ancient history on many of their lists. No wonder many kids prefer the honest escapism of computer games.