Toga! Toga! Toga!

There are armies massing in the west. They have elephants, horses, chariots, onagers and ballistae. They have standards flapping in the breeze, helmets glinting in the sunlight. They have blokes in strappy sandals and pleated miniskirts with only one thing on their minds: how to get you to cough up for a ticket to see them smacking each other about on the big screen.

There are armies massing in the west. They have elephants, horses, chariots, onagers and ballistae. They have standards flapping in the breeze, helmets glinting in the sunlight. They have blokes in strappy sandals and pleated miniskirts with only one thing on their minds: how to get you to cough up for a ticket to see them smacking each other about on the big screen.

Hollywood didn't plan for the resuscitation of the sword-and-sandal epic, but it's happening anyway. Conventional movie business wisdom says it's bad economics. The blockbusters that squat in our multiplexes every summer are usually crafted to very strict specifications: they must look good with a "2" or a "3" after their titles, to ensure that sequels will have the suckers boomeranging back for years to come. They must be sufficiently merchandisable to make most of their money back in broad daylight, filling Toys R Us with action figures, placing game cards in the sweaty palms of schoolboys and holograms into boxes of Frosties, and providing suitable themes for branded cans of spaghetti hoops. Spiderman and the characters from Star Wars can do this with ease, but Roman epics are not nearly so commercially compliant. Dreamworks wouldn't be able to make Gladiator 2 – which was this week revealed to be "in the pipeline" – without fiddling some corny stunt involving twin brothers and a kindly old shepherd. Nobody would rush out to buy honey-and-dormouse flavour spaghetti. McDonald's couldn't give away plastic viaducts with Happy Meals. Which is why such movies are a big financial risk, and bankrupt as many film companies as they enrich.

And yet, evidence for the coming boom in such pictures is being trumpeted from Hollywood's studio walls. Eighteen months ago, every exec in town decided they wanted their share of the $458m spoils Gladiator extracted in tribute from the world's cinema-goers. All those forgotten scripts with a chariot-racing scene and a cameo for Derek Jacobi were rescued from filing cabinets and pored over by teams of screenwriters. Now Hollywood's flesh-traders are putting faces to names, deciding whether Jennifer Aniston would make a cool Octavia, or Freddie Prinze Jnr a neat Diocletian.

Enumerating all of these projects would tax the memory of Homer. But here they are, like those pages and pages of ships in the first book of The Iliad. Two major studios are developing movies about the Battle of Thermopylae: Universal's version, it's thought, will see George Clooney lead his 300 Spartans into battle against the Persians. At Warner Brothers, Wolfgang Petersen's Troy will see Brad Pitt's Achilles spearing Eric Bana's Hector up the Dardanelles. (Bana has just played the Hulk for Ang Lee, so ought to fill his armour nicely.)

Sony Pictures is starring Vin Diesel in the title role of Hannibal – the Carthaginian one who marches with elephants, not the Welsh one who makes fricassées with human cerebra – and both Columbia and Fox have Hannibal pictures in development. James Cameron, who, like Alexander the Great, has been proclaimed conqueror of the known world, is working on a vaguely historical epic about the Amazons: Hollywood's tallest actresses are now honing their archery skills, but are expected to stop short of booking into an upscale tripe-slicing clinic for a designer mastectomy.

And here's where it starts to get complicated: a whole phalanx of Alexander the Greats may soon be marching into cinemas. Oliver Stone is planning a biopic of the conqueror. (His first choice for the role – the tousled-haired surf person Heath Ledger – has deserted, but Colin Farrell from Minority Report has declared himself happy to inherit Ledger's aspis.) The US cable channel HBO has announced a 10-part drama series that will also recount the career of the ancient world's most celebrated general, using the fiction of Mary Renault as its principal source. And until recently, Martin Scorsese was plotting his own big-screen version of the same story, which Leonardo DiCaprio was tipped to lead. Inevitably, a rival commander has risen to take his place: Baz Luhrmann, the director of Moulin Rouge, who has gone public about his decade-long desire to film Alexander's life. Like Scorsese, he wants DiCaprio in the lead role. Shooting is scheduled to begin in Morocco in the spring, using a script based on a trilogy of semi-academic beach books by Valerio Manfredi. In 2004, the theme of the summer will be Macedonian soldiers who charge around Asia Minor shagging each other and kebabbing the Lydians.

In the late 1950s, a picture like any one of the above would have been referred to as a "peplum". A pejorative coined by French critics, it refers to the micro-mini togas that fluttered around the thighs of the genre's beefcake heroes: bodybuilders such as Steve Reeves, Reg Park and Gordon Mitchell, men with thighs like flitches of bacon, who did battle with stop-motion monsters and armies of inaccurately-costumed extras. The films were shot in Italy, but the stars were all from Muscle Beach. Mitchell, for instance, was a Santa Monica bench-presser who, in 1956, took a job as a chorus boy in Mae West's touring stage show. As West shimmied through her songs and stand-up schtick, Mitchell would yank off his floor-length cape and give her a deltoid to rest upon. Back in Santa Monica, he spotted an ad in his local gym that read, "Herculeses required". He got the gig, and spent the next three decades in Rome, striding around in cheaply-made epics shot in the more desiccated parts of Italy. These films paid little heed to mythographical niceties, and would customarily pit figures such as Goliath, Atlas and Macistes against implacable enemies from other cultural traditions: Hercules vs the Vampires (1961) was a particularly peculiar example.

The origin of these entertainments, however, is much older than Steve Reeves's loincloth. The peplum was a way of packaging beefcake without causing its consumers any embarrassment, and was part of a long tradition of serving up the spectacle of the male body with classical trimmings. In the 1890s, the celebrated Victorian bodybuilder Eugen Sandow was rarely photographed without a pair of Roman sandals, an Ionic column and a ream of leopardskin. Although he would customarily powder himself with marble dust and allow spectators to have a feel of his gluteus maximus, there was nothing particularly sleazy about a Sandow event: he even persuaded Sir Arthur Conan Doyle to help him judge a body-building competition at the Royal Albert Hall. "Mr Sandow fairly went down on his hands and knees to examine the nether limbs of the men," wrote one commentator, describing how 15,000 spectators looked on "with breathless interest". (A Mr William L Murray of Nottingham walked off with the gold statuette, as the band struck up "See the Conquering Hero Comes".)

You can also see the peplum taking shape in glamorously vulgar late-19th-century popular art: luxurious representations of arena, bathhouse and slave-market scenes with an emphasis on naked thighs and calves. Lawrence Alma-Tadema is usually hailed as the prime exponent of the genre, but one of his pupils, the deliciously-named Herbert Schmalz, painted one of the most influential examples. His picture, Faithful unto Death (1888) is like a Hollywood toga epic contained on a single canvas. To the left of the frame, a huddle of naked victims strapped to a line of Pagan totems, cowering in terror and praying monotheistic prayers; to the right, an ominous empty area, suggesting the arrival of something red-clawed and randy for Christian innards. Schmalz's image can be seen imprinted upon the work of Hollywood's first and greatest proponent of the Roman epic, Cecil B DeMille. When Christians are thrown to the lions in The Sign of the Cross (1932), Schmalz, as it were, fills the screen.

So is the imminent revival of the genre anything more than a predictable rotation of the wheel of fashion? Baz Luhrmann, rather worryingly, sees the trend as a product of America's growing estrangement from the Islamic world. "It was the first time that the pendulum swung away from eastern culture," he has said. "What's going on in the world today is directly applicable to Alexander's time. The level of contemporary resonance is unbelievable. But for Alexander the Great there would not be the Western culture that we have today."

So when the West feels under threat, this theory goes, the toga acts as a kind of comfort blanket. Perhaps the act of going to the cinema to gaze upon European generals routing the Persian army might, for some audiences, offer a nostalgic reaffirmation of Western power. But I'm not sure whether it's the principal reason why there are so many of these films in pre-production. Most of Luhrmann's movies could be read as celebrations of occidental culture: when an imam imagines Hell, it's probably much like the final number from Moulin Rouge.

Better, I think, to look for an explanation in the everyday megalomanias of film-producing people. The return of the Roman epic just happens to dovetail beautifully with the native self-importance of film producers and big-shot directors. Producers don't back toga epics because they read a lot of Plutarch, or because they know that a big-screen version of Samuel Huntington's The Clash of Civilizations would be box office hemlock. They back them to wow audiences and Academy members into submission with a display of power and excess; to prove they can muster more extras, more trumpets, more standards, more ostrich feathers, more lions and more Praetorian guards than anyone else with whom they're ever likely to have lunch. That's why they take the huge financial risk. They get a kick out of seeing credit-rolls thick with lists of tiger-wranglers, elephant-handlers and suppliers of stuffed nightingales. They like making ancient cities rise and fall, particularly when CGI effects mean they no longer have to source a couple of thousand bed sheets to wrap around a couple of thousand extras to make an arena scene convincing. Rome can now spring, ready- formed, from the hard disk of some Hollywood pixel-jiggler in less than a day.

It's an ambition that Nero would have appreciated, and I suspect the admiration would have been mutual. When Roman emperors launched their gladiatorial games, they employed their armies to perform an eye-catching carnival parade through the heart of the city; they deluged the populace with free nibbles; they invited them to gawp at their star performers using crumpet forks and an eel-net to fight some ferocious beast. If the day went well, the emperor was hailed as a god, and avoided being poisoned for a few more months. Hollywood producers, after seducing us into goggling at a comparable display of extravagant spectacle, watch their box-office figures bloat, and – once award-ceremony season comes – start clearing space on their mantelpieces. Harvey Weinstein and the emperor Heliogabalus? You couldn't slide a lark's tongue between them.