However, the terraces were not perfect, as studies of the land show that there were landslides that happened during the construction of Machu Picchu. Still visible are places where the terraces were shifted by landslides and then stabilized by the Inca as they continued to build around the area. It is estimated that the area around the site has received more than of rain per year since AD 1450, which was more than needed to support crop growth there. Because of the large amount of rainfall at Machu Picchu, it was found that irrigation was not needed for the terraces. The terraces received so much rain that they were built by Incan engineers specifically to allow for ample drainage of the extra water. Excavation and soil analyses done by Kenneth Wright  in the 90s showed that the terraces were built in layers, with a bottom layer of larger stones covered by loose gravel. On top of the gravel was a layer of mixed sand and gravel packed together, with rich topsoil covering all of that. It was shown that the topsoil was probably moved from the valley floor to the terraces because it was much better than the soil higher up the mountain. However, it has been found that the terrace farming area makes up only about of land, and a study of the soil around the terraces showed that what was grown there was mostly corn and potatoes, which was not enough to support the 750+ people living at Machu Picchu. This explains why when studies were done on the food that the Inca ate at Machu Picchu, it was found that most of what they ate was imported from the surrounding valleys and farther afield. Even though Machu Picchu was located only about from the Inca capital in Cusco, the Spanish never found it and so did not plunder or destroy it, as they did many other sites. The conquistadors had notes of a place called "Piccho", although no record of a Spanish visit exists. Unlike other locations, sacred rocks often defaced by the conquistadors remain untouched at Machu Picchu. Over the centuries, the surrounding jungle overgrew the site, and few outside the immediate area knew of its existence. The site may have been discovered and plundered in 1867 by a German businessman, Augusto Berns. Some evidence indicates that the German engineer J. M. von Hassel arrived earlier. Maps show references to Machu Picchu as early as 1874. In 1911 American historian and explorer Hiram Bingham traveled the region looking for the old Inca capital and was led to Machu Picchu by a villager, Melchor Arteaga.