I saw a salamander the other night. This is, I believe, like seeing eternity. I had heard that they are common in the Dordogne, yet in 23 years here I've never seen one before.

The salamander is a heraldic, almost mythical, beast; a symbol of courage and fidelity because of the age-old belief that it can survive the heat of fire. This is nonsense, of course, as anyone would know who tried the experiment: a salamander dies in fire just like anything else. Yet its supernatural reputation has survived for thousands of years T H White (author of The Sword in the Stone) was fascinated by medieval beliefs. He repeated the old fable in his Book of Beasts: 'This animal (the salamander) is the only one which puts the flames out, fire-fighting.

Indeed, it lives in the middle of the blaze without being hurt and without being burnt - and not only because the fire does not consume it, but because it actually puts out the fire itself.'

Aristotle said something similar a couple of thousand years earlier: 'The salamander not only walks through fire but puts it out in doing so.' The belief presumably came about because, as Pliny's Natural History claims, 'It is so chilly that it puts out fire by contact, as ice does.'

It is true that salamanders are chilly; their bodies are covered with skin and not, like other lizards, with scales. And their preference for cold, wet hiding places makes them clammy to the touch. Pliny must have observed salamanders at first hand, for he describes them absolutely accurately as: 'A creature shaped like a lizard and covered in spots, never appearing except in great rains and disappearing in fine weather.'

I finally saw my first salamander at 5.30 the other morning. It had rained for most of the night and was still quite dark: ideal conditions for salamanders to make an appearance, less ideal for me. But my son, having spent the weekend with us, had to be up early to return on his motorbike to Angouleme where he is working on a film, to be on set by 8.30. I got up early, too, to warm some coffee and croissants before saying goodbye. He went outside to check on his bike and came back very excited. 'Quick, come and see] A salamander]'

It was about 12cms long and looked like a stumpy lizard, with a short tail, blunt head and abbreviated limbs. It moved in a cumbersome crawl very different from the elongated lizards that flicker swiftly along stones and roof-tiles to bask in the autumn sunshine. We shone a torch to get a better look and the salamander tried awkwardly, almost blindly, to avoid the beam.

Its shiny, moist skin was brilliantly patterned in gleaming black and yellow. It did indeed look like some heraldic beast.

A few years ago a friend reported seeing hundreds of them near here as she drove back home after dinner. They were crossing the road, again on a rainy night, carpeting the road in a thick, slow-moving mass. I now assume, having read up on salamanders, that she saw them on the one night of the year when they all congregate to mate.

Conditions must be perfect for the salamanders' big night. The ground must be damp but not frozen, the temperature at least 6C, and there must be steady rain. Then every salamander hidden in a state close to hibernation in tree trunks and mossy undergrowth miraculously rouses itself and makes its way to the lowest available wet area: a pond, ideally. Here, in their hundreds, the salamanders have their annual mass orgy. It lasts about one day and then they return to their solitary lives.

This simultaneous mating is a risky business. Conditions may not be ideal for the required erotic frenzy, and breeding may scarcely take place. This could help explain the salamander's longevity: most varieties (and there are more than 300, mostly in Europe and America) live for some 20 years.

Alternatively, their route may cross a road and not all motorists will be as captivated as my friend was, and stop to let them pass. In this case, mass slaughter may occur.

But now their survival is threatened by something much more serious than cars on country roads. The continued existence of these strange and beautiful beasts, whose symbolic image appears on countless coats-of-arms, appears to be at risk from the thinning of the ozone layer and pollution of their habitats. Scientists all over the world are now recording a drastic drop in their numbers.

The salamander is one of the oldest living creatures on this earth; it is as close as the rationalist gets to contact with eternity. It was the first animal to live on land as well as in water. It preceded by 200 million years, and has long outlived, its contemporary, the dinosaur. If the salamander, after nearly 400 million years, can no longer endure this polluted planet, then what hope is there for the rest of us?

David Wake, an American zoologist from Berkeley in California, has been studying salamanders in the Rocky Mountains. He has monitored the downward trend in numbers with increasing dismay.

'These amphibians are tough critters,' he says. 'They survived whatever wiped out the dinosaurs and they have thrived through the age of mammals. If they start to check out now, we'd better take it seriously.

'Salamanders are the miners' canary; and now the canary is ceasing to sing.'

Maggie Brown is away.