The Vespa is back.

That chic little Italian scooter that Audrey Hepburn used to whistle around the streets of Rome in the Academy Award-winning film "Roman Holiday" is making its re-entry in a big way.

The Vespa became an icon of Italian life in the 1950s and 1960s. But it took an American film director to make it internationally famous. The Vespa scenes in William Wilder’s Roman Holiday last barely three minutes, but they're the best thing in the film. Audrey Hepburn is the innocent princess, briefly and anonymously escaping her duties; an American journalist, Gregory Peck, recognises her and scents a story. He offers to show her Rome on the back of his Vespa.

The scene starts conventionally, with Hepburn sitting side-saddle, as they tour the Coliseum. As soon as Peck dismounts, she, not even a learner, grabs the controls and weaves the Vespa erratically through the plazas, causing havoc as she overturns fruit stalls, cafe tables and artists' easels. Hotly pursued by the police, the expression on her face is one of pure joy. She is experiencing that "freedom through mobility" for the first time, with herself -- however shakily -- in command. It is a liberation from her dutiful life and an assertion of her freedom, even, perhaps, to fall in love. Roman Holiday says this: everything they've been telling you about the Vespa is wonderfully true.

The Rome in Fellini's La Dolce Vita, in 1961, has an altogether darker mein than Hepburn and Peck's untroubled, romantic city of eight years before. There are no innocents in the fast society that the gossip columnist played by Marcello Mastroianni inhabits. The Vespas buzz around more sinisterly, ridden by the parasite snappers we now call paparazzi--a name derived from the photographer character Paparazzo. The scooter's ability to reach places not as easily or quickly attainable by car makes it the ideal instrument of intrusion.

There is a scene in La Dolce Vitain which the press gets to hear of a man's tragic death out in the suburbs. His wife does not yet know. Hacks and photographers assemble outside her house to await her return, tell her the news and photograph her reaction. Slowly the Vespas swarm around their prey; their task over, they zoom away in seconds. The Vespa has become a vehicle of oppression.

In Britain, for a few years in the early 1960s, the scooter became not just a cheap conveyance but a badge of social belonging. There were two ways to tell a mod from a rocker: clothes and transport. The rockers wore leathers and rode motorbikes; the mods had sharp suits and rode scooters. Franc Roddam's 1979 film Quadrophenia, inspired by The Who's 1973 album, was cinema's principal homage to the unmissed mods-and-rockers era. The unattractively aggressive Jimmy uses his scooter for clubbing, scoring drugs, gatecrashing parties and trying to impress the girls. He prepares to join a mass ride to Brighton, in expectation of a seafront battle with rockers. The entire screen is filled with Vespas (and, to be fair, the rival make, Lambretta) bearing down purposefully towards Brighton like a horde of migratory birds in an Attenborough wildlife shoot.

There, Jimmy sees the scooter of his dreams, a shiny customised Vespa encrusted with lights and wing-mirrors belonging to the most modish and good-looking mod of them all (played by Sting). Later, he sees the bike again; its owner, he realises, is just a lowly hotel bellboy. Disillusioned and dispirited, he steals the scooter and, after a frenetic ride on the clifftops, steers the machine deliberately over the edge. As they start their fall, rider and scooter part; it is the Vespa, not Jimmy, we watch tumbling into the sea. In the last, lingering scene it is the Vespa we see lying broken on the rocks below: a generation's dreams consigned to oblivion, no longer an instrument of liberty, but a symbol of death.

Not until 1994 did the Vespa resume its lighter, happier role in cinema. The first segment of Nanni Moretti's Caro Diario (Dear Diary) -- which won him that year's best director award at Cannes -- consists entirely of a Sunday afternoon outing on a Vespa to some of Rome's lesser known quarters. Moretti rides and comments wryly as he looks at buildings and housing developments, tries to learn flash-dancing, accosts strangers, watches an objectionably violent film, finds a critic who had praised it and tortures him with readings from his past reviews.

In the stunning final sequence, lasting more than five minutes without words, only a Keith Jarrett score in the background, the camera follows Moretti's Vespa as he rides to find the spot where Pier Paolo Pasolini was murdered. There are no frontal shots of rider or scooter, only back views as they negotiate the bleak and miserable seaside landscape to the neglected concrete sculpture that marks the spot. The scene ends abruptly. The Vespa has been vindicated. It has transported its rider over a range of emotions, from whimsy to anger and sadness. Fifty years on, it still delivers freedom.