Our ancestors have accomplished many magnificent works even with their limited means. South America in particular is a mysterious land with many such examples. There are evidences of human life in this continent that dates back to 9000 BC. So, it is natural to have many such finds that are reminiscent of that era like the mysterious holes of Pisco Valley.
There are a series of about 5000-6000 man sized holes found in the Pisco Valley on the Nazca Plateau in Peru. They are band of holes also known as Monte Sierpe(Serpent mountains) in Spanish or Cerro Viruela( smallpox hill). The band extends in a north-south orientation over an uneven terrain starting from the edge of a valley and up to a hill for about 1.5km.
Their arrangement is in the form of discernable blocks or segments along a band. The average width between them is about 19 meters. There are not enough evidences to prove the reason for their construction. Although speculations of it being defensive positions, grave sites, Incan granaries and even an extraterrestrial effect is quite prevalent.
The site garnered public attention when an aviator Robert Shippes published an aerial photograph of it in National Geographic in 1933. Victor Wolfgang Von Hagen officially surveyed the area in 1953 and made a report about them in "The Royal Road of the Inca", that they were pre-Inca graves. According to him there were over 5000 such circular stones lined in rows and marched up the 50° angle to the slope called Mt.Sierpe. They were of the same construction as that of those graves from which mummies, weaves and potteries have been excavated.
So, many people concluded them to be used for the same purpose but unfortunately no corroborating evidence can be found out as many of such holes have been filled and run over due to construction of roads. Archaeologist John Ayslop wrote in his 1984 book, "The Inca Road System", that these holes sometimes semi- subterranean, may have been used for storage.
Such structures are also found in the Peruvian south coast in the sites Quebrada de la Voca and at Tambo Colorado. As these structures are mainly constructed near the point where the Inca coastal road crosses the road to the highlands, it is assumed that they might be one of the empire's larger storage units.
In 2015, archaeologists from UCLA used drone aircraft photography to create a detailed map. According to their hypothesis, they could have been used to measure produce that had to be given as a tribute to the Inca state. The measurements might have been recorded on Incan "Khipus" and then reported to the government officials. Further studies are being done to detect pollens or phytoliths to confirm this supposition.
There have not been any artifacts, bones or any other human remains, recovered to prove that they were used as graves. Considering the size of the holes and the strenuous task of carving them on the ground it is unlikely why the inhabitants would have used them to store grams when there were other efficient and easier ways to do that.
Due to lack of sufficient evidence, the mystery of the origin of those mysterious holes still eludes us. It is hopeful that further research can unveil the truth.