Avoid the main tourist sites and you'll discover a city full of unexpected pleasures. By Michael Mewshaw
With some cities even first-time visitors have the sense of being blissfully wed. But Rome is not the type of town that induces feelings of drowsy domesticity and conjugal joy. Ever the demanding mistress, it insists on being taken on its own terms and visitors who try to impose their expectations do so at the peril of disappointment.

Yet for all its fickleness, it remains resolutely true to itself and has resisted changes more than any other European capital. Over the centuries, it has assimilated invaders, civilised barbarians, taken the measure of millions of travellers, and managed to retain its irrepressibly exuberant character.

The marmoreal splendour of the Spanish Steps, the weathered, time-worked stones of the Forum and Coliseum, the domed vastness of St Peter's - so many sites yield new and unanticipated pleasures on each trip. But the most riveting images are those that a traveller catches out of the corner of an eye. Two carabinieri on horseback come cantering down the Corso, clip-clopping through stalled rush-hour traffic like elegantly uniformed ghosts reincarnated from the last century. On wet mornings, the city's slabs of aged marble sprout veins of green moss, and in abandoned piazzas puddles of water slowly expand into lakes. After the first warm spring rain, the leafless black vines that dangle from balcony railings like threadbare rugs suddenly turn into magic carpets of flowers.

A collision of the ancient and the evanescent, the sacred and the profane, the sublime and the bizarre, Rome's contradictions sometimes suggest the sort of surrealism seen in Fellini's films. The Pantheon, for instance, is one of the most celebrated and best preserved antiquities. Constructed between 27 and 25BC by Marcus Agrippa, rebuilt by the Emperor Hadrian 150 years later, and often modified over succeeding aeons, this pagan temple, which served as a Christian church before it became a tourist icon, is a marvel of early architecture. Its dome was not surpassed in size until the 20th century. Yet while it exemplifies for scholars the measured serenity of the classical spirit, the Pantheon and its surroundings are simultaneously a buzzing hive of contemporary life.

Thronged by people, the portico serves as a meeting place for lovers, an improvised soccer pitch for impetuous boys who dervish among the massive pillars, and a home base for a toothless old crone who has been selling flowers there for as long as anybody can remember.

In front of the Pantheon, Piazza della Rotonda reverberates with motorbikes, street musicians, and the antiphonal chorus of impatient customers and harried waiters at outdoor cafes.

On Via dei Cestari, the shop windows seem to parody the designer wear on display along Via Condotti. Instead of Gucci shoes and custom-made suits, it specialises in religious garb; smiling mannequins show off this season's fashions for nuns and priests. Cassocks, sensible socks and shoes, and canonical underwear are on sale.

Via dei Cestari ends at Largo di Torre Argentina, a fenced-in square with a sunken space at its centre punctuated by the ruins of four temples, a red brick tower and a copse of cypress and pine trees rooted in crumbling rock. It is difficult to imagine a better symbol of the city, for this one spot boasts all of the Roman hallmarks. There are imperial remains as meticulously tended as a backyard garden, stray cats living fat and happy amid the splintered stones, dotty old ladies and gents who show up every day to feed the cats plates of pasta, tourists decked out in the flashy plumage of birds of paradise, and roaring around the spectacle there is a chaos of traffic spewing pollution that threatens to kill off the cats and trees, ruin the ruins and drive away the people.

The Jewish ghetto offers some relief from internal combustion engines, and on damp nights when the cobblestones gleam like the scales of carp, it's a great pleasure to stroll past dimly lit, hole-in-the-wall restaurants that serve traditional Italian-Jewish fare, such as deep-fat fried artichokes and cod.

Rome has other enclaves of privacy and quiet. The best of them is an island, Isola Tiberina, in the middle of the Tiber between the Jewish ghetto and Trastevere. Roughly the size and shape of an ocean-going ship, the island has for ages been renowned for its healing powers. Thousands of years ago it was the setting for a Temple of Aesculapius, a place where the ill gathered to pray for miraculous cures. Today, it boasts a hospital, a museum, a sculpture garden and marble-covered banks that attract lovers, fishermen and, of course, refugees from the urban frenzy.

As is the case in any tempestuous love affair, it is possible to get impatient with Rome, to feel a cold wash of objectivity quell one's ardour, to tire of its narcissistic demands, incessant mood swings, and indifference to straight reasoning. But there is something about it that continues to defy description and surpass understanding. Rome is eternal, and so is its hold on everyone who has ever submitted to its seductive embrace.

six suggestions for a weekend in Rome

Flights are more expensive than you might think, given that Rome is only a two-hour trip from Heathrow. The price to beat is pounds 262.30, the lowest official return fare on British Airways. Try Italy Sky Shuttle (0181-748 1333) and other discount agents.

Travel to the city from Leonardo da Vinci/Fiumicino airport on the hourly train to Termini station, price 12,000 lire (pounds 4.80). Cheap charters arrive at Ciampino airport, closer and cheaper to the city.

Sleep cheaply at the Albergo Pomezia, in the centre of the city at via dei Chiavari 12 (00 39 6 686 1371). A room costs 70,000 lire (pounds 28) single/90,000 lire (pounds 36) double.

Ask the Italian State Tourist Office, 1 Princes Street, London W1R 8AY (0171-408 1254) for its excellent free map and literature on Rome.

Escape the crowds by heading north for an hour to Bracciano, which bestows its name on an ancient town and beautiful lake.

Beware the most blatant robbers in the world - the children who hang around Termini station grabbing at tourists' possessions. Their age renders them immune to prosecution.