In its heyday, lions lunched on humans as a spectator sport. Now, writes Andrew Gumbel, man is biting back, along with the elements, and the Colosseum is crumbling
On a balmy recent spring afternoon in Rome, a sudden commotion seized hold of the crowds ambling their way around the Colosseum. One man swore he had seen some fragments of stonework tumbling down from the dizzy heights of the building's northern flank. A cluster of other visitors gathered round to look for themselves. Someone even called the fire brigade.

False alarm, said the authorities, you must have been imagining things. But two hours later, the whole charade began again. This time, a tourist munching a sandwich fancied he had seen one of the Colosseum's many cracks widening. The fire brigade received another emergency call, and once again they felt themselves obliged to explain that every stone holding up Rome's emblematic monument was monitored by experts. Constantly. There was really nothing to be alarmed about.

And yet the Colosseum is an alarming place, especially for those who set eyes on it for the first time. If it was in heritage-conscious London, it would no doubt be isolated from the bustle of the modern city, surrounded by safety cordons and adorned with signs asking visitors not to take food or drink into a site at once so sacred and so profane. There might even be a special underground train taking visitors through the bowels of the stadium on a "Colosseum Experience", complete with waxwork gladiators, stuffed wild beasts and a soundtrack reproducing the cheers and hideous screams of ancient times.

But this is Rome, and the Colosseum you get is unapologetic, and all too palpably falling to pieces. Approach from one side, and you have to brave one of the most dangerous road crossings in the city, with Fiats and tourist buses careering around a tight, two-lane corner on the Via San Gregorio. Approach from the other side, and you are accosted by gypsy children, hustlers passing themselves off as authorised tourist guides, overpriced sandwich and soft drinks sellers, not to mention a sizeable percentage of the population of eastern Europe spilling out of their rickety tour coaches.

And that's before you even get inside. You can't walk out into the arena because the floor has been entirely eroded. You can barely make your way up into the stands to get a spectator's-eye view because, again, large chunks of alleyway simply are not there and many of the seats periodically blocked off by scaffolding. You read in your guidebooks all those ghoulish tales of perverse blood-sport and human sacrifice, but in reality you have to use your imagination in situ almost as much as you do when perusing the written page.

It takes a while to realise that the whole point of the Colosseum is that it is falling to pieces, indeed that it has been falling to pieces almost since the day it was built. Its strength derives from the fact that it is still standing despite the many vicissitudes of its history; its fascination the paradoxical notion of an irreversible decline preserved for ever.

The time-honoured proverb says that as long as the Colosseum stands, Rome will stand, and that when the Colosseum falls, not only will Rome fall, but the world will pass away with it. That may sound like an excuse for a dose of pre-millennial gloom, but it is worth bearing in mind that by the time the Venerable Bede first recorded the proverb in the eighth century, the Colosseum had already been ravaged by foreign invasions, fire, lightning, earthquakes and general looting. When Byron gave his own version of the saying in the Fourth Canto of "Childe Harold" more large chunks of Travertine marble had been plundered by Renaissance popes to build palaces, bridges and even part of St Peter's.

The Romans themselves are at a loss to explain the durability of their most famous monument, the "ruin to beat all ruins" as one guidebook justly calls it. But unlike those tourists who imagined it was all about to come tumbling down around them the other day, the Romans have tended to tell themselves stories magnifying the mysterious longevity of the place. How to explain, for example, all the holes that pockmark every arch and every column of the exterior?

Historians and archeologists will tell you that these were made by metal cramps used to erect the amphitheatre in the first place; the various accounts of their disappearance vary from the routine (they were removed and used for other building projects according to Roman architectural practice) to the criminal (they were looted by Pope Constans II in the seventh century).

But Roman legend tells quite a different story. When the Barbarians took over Rome, so the story goes, they resolved to destroy the Colosseum as the supreme symbol of the power of the old empire. The way they decided to do it was to gouge little holes all over the building and fill them with gunpowder in the hopes of blasting the whole thing to smithereens. The fuses were duly set, but the Colosseum did not cede so much as a single stone in the ensuing explosion. Awed by their clamorous failure, the Barbarians concluded that the place was indestructible and made no further attempts to attack it.

Never mind that this story is quite implausible - to start with, gunpowder was quite unknown to the hordes of Goths, Huns and Vandals who sacked Rome repeatedly over the course of the fifth century. The point is that the Colosseum is looked upon as a charmed monument, something that bestows good luck on the whole city. The place may now be besieged by pollution, traffic and endless epidemics of weeds, but they seem no more threatening than the ravages of centuries gone by. There are even plans to use the Colosseum in the 2004 Olympic Games, should Rome be lucky enough to win them, as a backdrop to the wrestling event.

Perhaps the key to the Colosseum's charm is to take Byron's advice and avoid it by day altogether. You may miss out on the guts of the place, the animal cages and prison cells where the gladiators anxiously waited their turn in the days of Emperor Titus. But you also avoid the holes and pockmarks, the sad quarry of the proud stadium's stolen glories, the sense of one of the world's great wonders scarred and mutilated. Come instead by night, when the moonlight is these days supplemented by the soft orange glow of spotlighting that magically transforms the great hulk of brick and stone into the stuff of romantic dreams. As Byron wrote:

When the stars twinkle through the loops of time,

And the low night-breeze waves along the air

The garland forest, which the gray walls wear,

Like laurels on the first Caesar's head;

When the light shines serene but doth not glare,

Then in this magic circle raise the dead:

Heroes have trod this spot - 'tis on their dust ye tread.