Machu Picchu risks of landslides, earthquakes and injury due to decaying structures. Nude tourism is a recent trend, to the dismay of Peruvian officials. In several incidents, tourists were detained for posing for nude pictures or streaking across the site. Peru's Ministry of Culture denounced these acts for threatening Peru's cultural heritage. Cusco's Regional Director of Culture increased surveillance to end the practice. In January 2010, heavy rain caused flooding that buried or washed away roads and railways to Machu Picchu, trapping more than 2,000 locals and more than 2,000 tourists, later airlifted out to safety. Machu Picchu was temporarily closed, reopening
Machu Picchu prevent it from running down the mountain. Similar layering protected the large city center from flooding. Multiple canals and reserves provide water throughout the city that could be supplied to the terraces for irrigation and to prevent erosion and flooding. The Incas never used wheels in a practical way, although their use in toys shows that they knew the principle. The use of wheels in engineering may have been limited due to the lack of strong draft animals, steep terrain and dense vegetation. The approach to moving and placing the enormous stones remains uncertain, probably involving hundreds of men to