DEEP beneath the streets of Paris, police are playing a game of cat and mouse with a band of explorers who have turned the city's underground tunnels and chambers into their personal playground.

The so-called cataphiles, equipped with waders, torches and rucksacks, drop in through manholes to explore disused medieval quarries and catacombs, spray graffiti and throw parties.

"You can just as easily come across the chairman of a big French company as a scruffy punk," said Alex, a 24-year-old history student who has been sneaking in for three years.

In the pitch-black corridors 20 metres below ground, everyone goes by a pseudonym. Cataphiles with names like Bad Trip, Silence and Nexus leave fliers printed with drawings and poems tucked into crevices in the centuries-old stones.

"It's part of the idea, not knowing what people do in real life. It's like living a double life," Alex explained.

Down there, the temperature is a constant 15 degrees Celsius (59 degrees Fahrenheit) and the humidity 100 per cent.

While visitors line up at the official Paris catacombs museum to view mountains of skulls and bones extracted from overcrowded cemeteries, the clandestine groups prefer to strike out on their own.

At the weekend, up to 400 people can be found roaming through hushed galleries where 18th century plaques bear the names of old streets and royal engineers.

Skilled cataphiles elude police by ducking into corridors or moving in the dark. Some drop smoke bombs to cloud their tracks and deter newcomers they disparagingly refer to as "tourists".

Tough cops

Although the intruders keep a low profile, the recent discovery of a fully functioning underground cinema - complete with bar and toilet - has embarrassed the authorities in charge of patrolling the 300-km (185-mile) network.

The set-up, including electronic sensors that set off the sound of barking dogs, was the work of a brazen group that has also infiltrated the Paris metro and electricity grids. "Don't look for us," it said in a note.

Police Captain Luc Rougerie has little patience for pranks.

"Nobody has any business down there," he said at the headquarters of his division, which also includes rollerblading policemen and sharpshooters.

His mission is to bar access to sensitive sites and prevent people from getting lost or injured in the maze of corridors.

Specially trained officers conduct regular patrols and systematically issue a court summons to anyone they catch. Offenders risk fines ranging from 60 to 150 euros (US$75-185).

This rigid application of the law has left some nostalgic for the days of Jean-Claude Saratte, who tolerated experienced cataphiles and shared their passion. They in turn would tip him off if they saw anything unusual.

"He was surrounded by a parallel police of informers," said Alain Clement, co-editor of the "Atlas of Underground Paris".

Though a veteran cataphile himself, Clement deplores the vandalism that has flourished in the last 20 years.

"I went down there for the first time in 1973, and when I go these days and see the state of the quarries, it makes me sick," he said. "It's full of young people who go there to escape from society, to drink and smoke joints."

Secret helpers

Clement has founded a non-profit organization, approved by the state, to preserve a section of the quarries located underneath the Cochin hospital on the Left Bank.

Visitors enter through a yellow door by a car park and climb down seven flights of stairs to the warren, which volunteers are restoring by the light of sodium lamps.

There, Clement and his group meet regularly around a rough stone banquet table to fry up the mushrooms they grow underground.

Clement would like to see the rest of the quarries sealed for good, but he thinks authorities are reluctant to close the network due to fears that terrorists could strike in Europe.

"If the quarries were completely shut, there would be no way to control them. The cataphiles, in fact, are like a clandestine control network," Clement noted.

Police officials acknowledge that regular patrols are essential to prevent a potential attack, but deny that they secretly welcome the presence of cataphiles.

"The cataphile scene is very mixed and you have different groups that are opposed, which could potentially lead to violent clashes," Rougerie said, without elaborating.

Alex said the only tensions he had witnessed were between graffiti artists and those who want the quarries left intact, and those arguments were limited to verbal exchanges.

He believes that contrary to their bad reputation, most cataphiles care about preserving their underground kingdom, but are powerless against officials and property promoters who are pumping concrete into sections they want to seal off.

"The network is shrinking imperceptibly every year but in the end, in 50 or 100 years, it will be chopped up so that it is no longer accessible," he predicted.

(Agencies via Xinhua)