By Hannah Hennessy
BBC correspondent in Lima
Authorities in Peru have submitted a $130m plan to the UN's cultural arm, Unesco, to preserve the Inca citadel of Machu Picchu.
Machu Picchu generates substantial revenue
The UN body has warned Peru that the famous site might lose its world heritage status if they do not act to protect it.
Every year, hundreds of thousands of people visit Machu Picchu.
Nestled between three sacred mountains in the Andes, it is South America's best-known archaeological site.
But fame has taken its toll. Experts say unrestricted tourism and landslides have damaged the 15th Century citadel and the nearby Inca trail that leads to it.
Machu Picchu was discovered under thick forest by the American explorer Hiram Bingham in 1911.
But almost a century later, its future remains uncertain.
Unesco's warning that it could put the Machu Picchu on its list of at-risk sites forced Peruvian authorities to detail their plans to protect it.
The proposals in a 400-page report are believed to include satellite monitoring to measure earth movements and a daily limit of 2,500 tourists.
But critics say that figure is too high and similar to the number of people who troop through Machu Picchu every day.
Unesco is due to deliver its decision in June.
Authorities will be hoping that their proposals convince it Peru is prepared to do all it can to preserve one of the jewels of South America.