Angkor Wat is just one of the great monuments at risk from tourism, writes Mark MacKenzie

The celebrated temple complex, built in the 10th century, is not the only ancient monument to be suffering under an onslaught of visitors, but it is one of the more vulnerable. It currently draws about one million tourists a year, but estimates suggest that over the next few years visitor numbers could swell to as many as five million a year.

Such an increase in traffic is something the ancient sandstone structures are ill-equipped to cope with, according to John Stubbs, vice-president for field projects with the World Monuments Fund. A not-for-profit conservation organisation based in New York, the WMF was founded in 1965 with, says Stubbs, a simple mandate: to raise public awareness and save significant historic buildings throughout the world.

The WMF oversees 250 projects in 83 countries, preserving significant sites from the ravages of time. And Angkor Wat is on the critical list. Phnom Bakheng, a five-tier temple perched on a 65m-high hill, is one of the most imperilled of the 40 or so monuments in the area. The most prominent feature for several miles, Phnom Bakheng at sunset is regarded as the quintessential Angkor experience. And therein lies the problem.

"The complex has had a fairly rough life," says Stubbs. Even before the Communist guerrillas started shooting at it, the temple had to endure centuries of neglect in the humid jungle. Angkor Wat was placed on Unesco's list of World Heritage sites in 1992 after centuries of wear and tear had taken their toll.

Chief among Phnom Bakheng's problems is the parlous state of the temple's sandstone veneer. "It's falling away like icing falling off a cake," says Stubbs. And an ever-growing army of marauding tourists hardly helps. "Tour operators promote it more than they should and the numbers are getting out of control. There's a need to manage visitors as many don't appreciate how delicate the structures are."

Angkor's appeal makes it unlikely that operators will remove it from itineraries any time soon, but the fragility of the complex is not entirely lost on the industry. At least not according to Natalie Lewis, programme manager for South-east Asia with Cambodia specialist Audley Travel. "The guides we use are aware of the duty that tour operators have," she says.

The company was responsible for 1,000 room-night bookings in Siem Reap, Angkor's feeder town, last year and Lewis welcomes information on threats to specific monuments. "It's the kind of detail that doesn't always filter back to us," she says. "It's difficult to restrict our clients' movements when everybody else is doing it. We monitor the situation and try to respond where appropriate." After a recent ban on large coaches travelling through temple areas, for example, Audley began to encourage visitors to take in the sights by bike.

The WMF has spent the past 18 months devising a full restoration programme for Phnomh Bakheng. Stubbs puts the cost of repairs to the temple at about $3m. That is a lot for the WMF; its annual global budget, mostly raised from corporate and other donors, is only about $60m.

"There are various options but we're looking at a restoration that will last for 100 years," says Stubbs. "To a certain extent, we're trying to fool time but theoretically you can extend the life of almost anything depending on the nature of the fabric. In the short term, we'd like to see tourists directed to alternative sunset venues."

Audley Travel already promotes community projects among some of Angkor's lesser-known temples such as the Rolus group. "Heritage tourism is a double-edged sword," says Stubbs. "Visitor revenue is often a saviour and so there's always a great scramble for that money. The downside is overtouristed sites such as at Phnomh Bakheng, where the visitor experience is compromised."

"It's a difficult balancing act," concedes Lewis. "Angkor is a site everyone should see at some point in their life but at the same time it needs to be looked after."