Despite being one of the most important Inca monuments, hardly anything is yet known about Machu Picchu. There are still many questions that will probably never be answered. What was it? What was its purpose? When was it built? Why was it abandoned? Why did the Spanish conquerors never know about Machu Picchu? Was it still inhabited even long after the Spaniards had reached Cusco?, and many other such questions.

In a way, given its strategic location, it could have been a military centre, a defence post for controlling the likely rebellions by the "antis" or natives, or an advance post for the conquest of the forest area or Antisuyo.

It is also believed that it was the Inca's ideal resting place, or the major sanctuary devoted to the Inca Pachacutec, who saved the cuzqueños from the Chanca invasion. Or, as emerges from the discovery of an only-female cemetery, It might have been the secret home of the acllas or "royal virgins" devoted to the deities and serving the Incas.

As Luis Valcarcel claims, Machu Picchu may have been Vitcos, the legendary fortress guarded by Vilcabamba, due to the similarities between the Quechua words picchu and vitcos or pitcos. According to Luis Miguel Glave and Maria Isabel Remy, Machu Picchu corresponds to the Picho settlement, mentioned in an old document found in the Historical Archives of Cusco; then, it might have been located in the estates of the Inca Pachacutec.

According to Hiram Bingham, Machu Picchu could have been Tamputoco, the mythical cradle of the Inca elite. Later, he changed his mind and claimed that it could correspond to Vilcabamba, where Manco Inca and his dynasty dwelled after attempting to beat the Spanish invaders. In addition, given the amount of women's tombs found, he proposed that the last settlers were acllas or selected maidens that fled from Cusco when the Spaniards appeared, to hide in this remote area in order to perpetuate the ancient customs and rites.

Finally, Machu Picchu is said to have fulfilled the aims it was built for. It was used to shelter part of the Inca aristocracy after the Spanish conquest of Cusco in 1532. Being an unimportant agricultural centre far away from main roads, Machu Picchu remained unknown to the Spaniards; that is why it was not destroyed by the new conquerors. Once Tupac Amaru, the last Incan rebel, was captured, it had to be abandoned, since there was no longer any reason to stay there.

But, as yet, there are no certainties regarding its purpose. No 16th century chronicler mentions it. There are only hypotheses and conjectures. Since its discovery, Machu Picchu has remained an archaeological site shrouded in mystery. Its discovery simply triggered another mystery for archaeological science.

However, Machu Picchu is, without any doubt, one of the most important archaeological wonders of the world not only because it was built on a ridge of difficult access, but also because it is one of the few urban projects that merge perfectly with its natural surroundings. There are no doubts that these ruins are just as valuable for mankind as the other "Seven Wonders of the World". It must have been quite a task for the men of those times to build the majestic Citadel of Machu Picchu.