Sitting up in the clouds, the Inca citadel of Machu Picchu in the Peruvian Andean foothills is becoming a hazardous place to visit.

The wives of the mayors of Jersey City, N.J., and Cuzco, Peru, and two Dutch hikers were killed in two separate incidents recently on their way to the Inca sanctuary, which attracts thousands of tourists every year.Machu Picchu, which means "Old Mountain" in the Indian Quechua language, was the holy place of the Incas, who once ruled a huge empire stretching from what is now Peru to Chile. It has become one of Peru's top tourist attractions.

Until the early 17th century it was the place where the Inca lords, who were called the "Sons of the Sun," worshipped the mighty Sun God Inti and other deities, historians and archaeologists say.

Dutch tourists Josephine Helena Knuppe and Gerard Gilles de la Hayze were found dead in November in a remote part of the Inca Trail that runs from near Cuzco to Machu Picchu. They had been declared missing in early October, when they were probably attacked and killed by robbers, police said.

Within a week of the discovery of their decaying, half-naked bodies, the wives of the mayors of Jersey City and Cuzco were killed when a small train plummeted off a cliff six miles from Cuzco.

Anna Cucci and Doris Mayorga - traveling together as part of activities to make Jersey City and Cuzco sister cities - were killed and their husbands were among eight people injured in the crash, which authorities said may have been caused by sabotage.

Police found an iron bar on the track that the train apparently hit, propelling it over the 150-foot cliff. Authorities said they suspected Maoist Sendero Luminoso (Shining Path) guerrillas may have derailed the train in a protest against the government's economic policies.

The crash took place the same day as a 24-hour general strike called to protest an austerity package that sharply raised food and fuel prices.

The derailment was the first such incident since June 1986, when seven people, including an American woman and a West German couple, were killed by a bomb attack on a train packed with tourists in Cuzco shortly before it was due to leave for Machu Picchu. The authorities blamed the attack on Sendero.

Overlooked by the gold-hungry Spanish conquistadores who plundered the Incas' treasures, Machu Picchu lay covered by a green veil of jungle until an American explorer, Hiram Bingham, found it in 1911.

Bingham, a young professor of South American history, paid a native farmer a dollar to lead him to the city hidden in the Andean foothills, tourist guides said.

Under the sponsorship of Yale University and the National Geographic Society and with the help of 100 workers, Bingham spent four years clearing the ruins of jungle growth, mapping the sites and carefully studying its graves.

Archaeologists believe Machu Picchu was inhabited until the early 17th century and that its residents died of natural causes, leaving no descendants.

Every year hundreds of tourists trek to the ruins, a three-day hike from near Cuzco. People take this hazardous route because they want to see the best-preserved ruins of the Inca Empire.