Tourists love the enigmatic Inca citadel of Machu Picchu high in Peru's Andes. They may love it too much.

As the country prepares to celebrate the 100th anniversary of the rediscovery of the "Lost City of the Incas" on Thursday, archaeologists are warning that a heavy flow of visitors and poor administration are threatening one of the wonders of the world.

The Incas built Machu Picchu atop an Andean peak 7,970 feet (2,430 meters) high, with a breathtaking view across the inhospitable abysses that surround it. Some experts believe it was a refuge for one or more Inca rulers, others that it was a religious sanctuary.

The site receives an average of 1,800 visitors a day and the maximum allowed by authorities is 2,500. Already, the former farming village of Aguas Calientes that is used as a jumping-off point for tourists has grown into a town of 4,000 inhabitants with five-star hotels and restaurants.

In some places, authorities have noticed soil erosion and damage to vegetation, Juan Julio Garcia, regional director of Peru's culture ministry, told The Associated Press.

Tourism companies and some local officials constantly pressure authorities to allow even more tourists, arguing it would benefit local communities.
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FILE - In this April 1, 2010 file photo,... View Full Caption

Cultural guardians fear irreparable damages if the tourist flow surges, and they are especially concerned by official plans to build a highway to the remote 15th-century ruin.

Tourists now must reach Machu Picchu by foot or by a scenic, zigzagging narrow-gauge train ride.

"In one way or another, the train controls the flow (of tourists). There is a maximum capacity on the train and this maximum capacity determines how many people can reach the monument. In contrast, with a road, any person or tourism company can reach the site and try to enter the sanctuary," Garcia said.

But rains washed out the rail route in January 2010, trapping 4,000 tourists in the towns of Machu Picchu and Aguas Calientes for five days. Without road access to the area, the government had to airlift tourists out by helicopter. In Aguas Calientes, which serves as a tourist base for Machu Picchu, there were shortages of food.

In September, Peru's Congress approved construction of an access road to Machu Picchu.

That raised a red flag at UNESCO, which inscribed the Inca stronghold on its World Heritage list in 1983, boosting the site's fame and making it eligible for international technical support. The U.N. agency had already expressed concern about management of the site. It said in 2008 that there were "urgent problems with deforestation, the risk of landslides, uncontrolled urban development and illegal access to the sanctuary."

The U.N. agency threatened to put it on its list of endangered sites if the road project is not canceled, a move that would be a blow to Peru's prestige.

Peruvian tourism authorities insist they are protecting the monument. Carlos Zuniga, head of the Foreign Trade and Tourism office for the Cuzco region, said that officials have given UNESCO proof of concern for Machu Picchu by completing a plan for use of the sanctuary and by issuing a decree that funds generated by tourism to Machu Picchu be used in maintaining the site. Previously, earnings were sent to the central government in the capital, Lima.