For 2000 years Twmbarlwm has stood sentinel, defying even the Roman Legions but is now being destroyed by a new reckless and sometimes violent force. Mike Buckingham reports.

ITS precipitous flanks have withstood the attacks of rival Celtic clans and the soldiers of Vespasian's Roman Legions.The Normans, ever-watchful against the vengeful Welsh kept a vigil from its summit.

"But as things are going it will be the off-road bikers who will finally defeat the mountain" says Terry Evans of the Twmbarlwm Society, one of a small group who has pledged to save Gwent's most prominent landmark from a fate which even 2000 years of warfare have not wrought upon it.

Within five minutes of his passing the remark a white van bumps up the track leading from the Ty Sign estate disgorging a man and a group of children and youths. Three motorcycles are produced from the back of the van which are fired up with raucous barks.

A minute later the machines are speeding along the long track that leads to the summit a trail of mud and stones thrown up in their wake.

In these politically-correct times any mention of the fact that this once- beautiful place has suffered from being hard by high-density public housing is taboo but it doesn't alter facts.

From the parking area where the van has stopped a mound of litter six feet across has been collected. Someone has found it amusing to set fire to the mound and leave more empty lager cans and fast food wrappers as interest.

"There are good guys in this story" Terry, a graphic designer with his own business says." Gwent Police take us seriously. Police officers do come up here which has a deterrent effect.

"Some of the dirt bikers can be very nasty. I've had them trying to run me over. "I tell him that two years ago a dirt-biker in his forties on nearby Mynydd Maen drove his powerful bike straight at me, lashing out with a heavy boot.

Innocent walkers who try to reason with those engaged in criminal trespass will be lucky to get away with a mouthful of verbal filth.

We begin the half-mile walk to the summit. The scarred, bare and rutted track is at this point three to five yards wide the tyre tracks of the most recently-visiting vandals clearly showing.

Further up the strips of destroyed turf become narrower as the off-roaders each take their individual paths. Many bring their machines to the mountain in vans. Others, faces hidden by scarves or full-face helmets and their machines without tax and registration plates and therefore without insurance arrive via the public roads.

Such riders will quite openly use garage power-washes to rid their machines of mountain mud, safe in the knowledge that the odds are against being challenged by a patrolling police car. If the amount of damage is depressing when seen from ground level it is even more so from the air.

A year ago I flew over Twmbarlwm while my wife took pictures from the co-pilot's seat. A giant hairpin-shaped area of ripped turf extends back in the direction of Cwmbran with smaller tentacles of destruction running hither and thither between the largest areas of damage.

Half-way to the summit we find a spade dropped in the bracken. "Probably fallen off a four-by-four. You get those up here as well", Terry remarks. "You know, I'm not against people on motorcycles having fun. I ride a big road bike myself and can see how off-roading might be fun but why, I ask myself, at the cost of Gwent's most iconic mountain?"

Twmbarlwm was probably first occupied in the Bronze Age several hundred years before the birth of Christ but was certainly in use by the Iron Age, possibly as a corral for cattle or place of refuge in time of inter-tribal strife.

With the coming of the Romans it was defended by the Silures tribe which offered stiff resistance to Imperial war plans. The actual 'pimple' is the remains of a Norman observation post which would also have been in use at the time of the Armada when in all probability a signal-fire would have been situated there.

Until well within living memory miners would spend their holidays encamped on its flanks or amid the surrounding hills. Once there were grouse and skylarks. The grouse have long gone and skylark numbers are depleted along with other species which once made the mountain their home.

The bark of two-stroke engines and stink of burnt oil-petrol mixture is less agreeable to nature even than to humans.We arrive at the top where another kind of wilful damage can be seen.

An area of soil eight or nine feet across has been excavated. At first I think it is a sheep-scrape but Terry puts me right. "People try to bury cremation urns here" he says.

A young woman with her young family get nearer and nearer until they arrive, panting and faces stung by the cold, by our side. "We come from Llanmartin and it's our first time up here" she says. "It's beautiful."

Terry agrees and gives her a leaflet printed by the Twmbarlwm Society which details the society's work and asked walkers to report off-road vandals and if practicable, to use their mobile telephones to capture evidence.

Back down at the car park the adult rider and youths have finished their business of ripping up the mountain for the day and put the bikes back in the van. We take a picture but instead of being shamed the adult strikes a pose. His cockiness might be premature.

There are witnesses and the van's registration has been telephoned to the police. The process is more tortuous than many would like but persistent offences can result on the confiscation of bikes and van.

"You can't take pictures of us. I got kids here!" The gesturing adult shouts." A fine example to the children he is but that's what we're dealing with" Terry Evans says."It's an uphill fight if you excuse the unintentional pun."