Sometimes, though, the stage fades. Summer dust and traffic fumes, tourist crocodiles and dehydration do nothing for the dramatic effect. In order to bask in the full glow of Rome's theatricality, you need sharp edges and a raking light, plus the privilege of feeling that this is all being staged for your benefit. Which is why February is the best month to visit Rome.
Away from the autumn rains and the January freeze, February often surprises with its mildness. Some days you can even risk a T-shirt - though don't expect the locals to follow suit: Romans dress according to an abstract idea of the season, sweating happily in their furs. But most important, you can make and inwardly project your own film of the city without too much interference, and without being pigeon-holed as a tourist - the kiss of death for any budding virtual director. Romans are so busy getting on with their end-of-winter chores (shopping, dressing the kids up in absurdly expensive fancy-dress costumes for Carnevale) that they just don't see tourists at this time of year.
As an example of sheer staginess, Piazza del Popolo can hardly be beaten. Travellers from the north used to enter the city here, through the Porta del Popolo (these days you can only go through on foot or in the number 90 bus). The inscription Felici Fausto Ingressui ("For a happy and blessed entrance") commemorates one of the most splendid of many entrances, that of the prestige Catholic convert Queen Cristina of Sweden in 1655. I made my own first entrance through it some years ago - without the fanfares - having just been ditched by a carload of German hippies who had given me a lift down from Berlin.
The sudden shock of the obelisk of Ramses II above the water-spewing lions added by Napol-eon, the twin churches - subtly dissimilar - guarding the triton-fork of three straight roads that led, from left to right, to the den of artistic iniquity around the Spanish Steps, the political purgatory of Rome's town hall and the pilgrim's paradise of St Peter's: all this, plus the fact that my ideal woman was there on the steps, waiting for me, condemned me to a long and hopeless love affair with the city. If I'd come in by any other gate I might be in Ulan Bator by now.
But not everything is on the surface. Two other dramatic gems are hidden away inside the church of Santa Maria del Popolo. Caravaggio certainly knew a thing or two about the film director's main concerns: lighting, timing and dealing with actors. Placing his work in a gallery does not really do it justice - it needs to emerge from the shadows into light. As the coin drops in the light machine illuminating the Carasi Chapel, the Crucifixion of St Peter and the Conversion of St Paul leap out of the darkness, both frozen at a choreographed moment that has both a present and a past, like so many of the painter's compositions, and like so little that went before.
If Caravaggio represents the artist-as-film-director, Bernini was the master of town- planning-as-theatre. The Fontana dei Fiumi in Piazza Navona is a swaggering, high-Baroque set piece, with the four massive river gods below the obelisk, the swaying palm tree and the emaciated lion, stooping to drink. It also furnishes one of the hoariest of all tour-guide anecdotes: the hooded River Nile and the cringing River Plate are supposed to convey Bernini's belief that the adjacent church of Sant'Agnese in Agone, built by his "rival" Borromini, was in imminent danger of collapse. The fact that two years passed between the unveiling of Bernini's fountain (in 1651) and the start of work on Borromini's church is, of course, an ungenerous cavill.
Angels on bridges, conch-blowing tritons, playful obelisk-bearing elephants: Bernini did his best to bring his theatrical expertise to bear on the fabric of the Eternal City, providing it with a ground plan of sub-plots and denouments. This is a man, remember, who used real fire and floods in the masques and entertainments he organised, and who also encouraged audience participation. There is plenty of the latter in one of his most over-the-top works: the Cornaro Chapel in the church of Santa Maria della Vittoria. A crisp winter's morning is probably a good time to view this, as the central sculpture of the Ecstasy of Saint Teresa has been known to provoke hot flushes and palpitations. What is really astonishing about the piece, though, is not so much the physical nature of Teresa's ecstasy or the smirking angel about to pierce her breast with a decidedly profane- looking arrow, but the absorbed spectators sitting in theatre boxes around the side - members of the Cornaro family who commissioned the chapel. An 18th-century French visitor, President de Broseas, was unimpressed: "If that is divine love," he remarked, "I know what it is."
If Baroque Rome was a stage set, modern Rome is cinema. The Via Veneto may be only a shadow of its Dolce Vita self, but the Trevi fountain - built a century after Bernini but inspired by his work - is looking as sprightly as ever. Anybody thinking of emulating Anita Ekberg's late-night dip would be well advised to wear a wet suit beneath the ball dress. It was April when the scene was actually shot - April 1959 - and behind the cameras recording the mystic aqueous communion of Marcello and Anita was a crowd of curious onlookers, kept back by hassled policemen.
In later years Fellini preferred to reconstruct everything in the studio: he claimed that it was "more authentic" that way. For the motorway scene in Rome - which comes across as a surreal fantasy until you actually attempt to drive around the Gran Raccordo, Rome's M25 - he simply laid down half a kilometre of three-lane motorway at the Cinecitta studios, complete with signs, street lamps, prostitutes and bridges.
Anyone visiting Rome this February should grab the rare chance to go on a tour of Cinecitta, which is being thrown open to the public to celebrate a hundred years of Italian cinema. Here at last, beneath the back-lit umbrella pines, amid fragments of statuary left over from blockbusters like Ben Hur and Cleopatra, do the charms of this potentially disorienting city fall into place. St Peter's and the Roman Forum may be the big sights, but it is Cinecitta which offers the best key to an understanding of Rome. It unmasks the city as a dream factory.
Short breaks to Rome are offered by Kirker Europe (0171-231 3333), Time Off (0345 33 66 22) and Sunvil (0181-568 4499) from both London and Manchester. Prices start from around pounds 250 per person for three nights, bed and breakfast, staying in a two-star hotel.Reuse content