Machu Picchu is generally accepted to have been an Incan retreat, built in the middle of the 15th century on a barely accessible mountaintop of Peru about fifty miles northwest of Cuzco. It was apparently abandoned a century later and only brought to the attention of the outside world in 1911, when it was rediscovered by Hiram Bingham III (1875-1956).
In 2021 the use of a more advanced dating method (accelerator mass spectrometry) has pushed back the earliest date for the site by a couple of decades to 1420 AD(j).
Mark Adams, the American writer, wrote an account of his retracing of Bingham’s journey to Machu Picchu. Along with the narrative of his pilgrimage, Adams has also interwoven a valuable history of the region.
In 2013, a Polish-Peruvian team, while exploring a previously unexcavated building on the site, claimed to have discovered that the structure was astronomically aligned(a). The following year saw a newly discovered section of the Inca Road, which leads to Machu Picchu, announced by the Andina News Agency(c).
In July 2016, it was reported that what are considered pre-Inca petroglyphs were discovered in the Machu Picchu region(d)(e). Research is proceeding.
The siting of the sanctuary has been something of a mystery, Recent research suggests that the existence of geological faults that lie beneath it may offer some of the answers. Rualdo Menegat, a Brazilian geologist, presented a paper to the Geological Society of America’s Annual meeting in Phoenix, in which he claims that the Incas deliberately chose to build Machu Picchu and some of their cities where tectonic faults meet!(h)
It was revealed in 2019 that work had commenced on the building of a new interational airport to service Machu Picchu, a development that has been vigorously opposed as a threat to the already fragile site. It is worth noting that in 2017, 1.5 million visitors, nearly twice the limit recommended by UNESCO, came to Machu Picchu(g).
Also in 2019, it was announced that an even older Inca site was discovered 1,500 metres higher than Machu Picchu using LiDar(i).
Some pathetic attempts have been made to link Machu Picchu with Atlantis. One of them claims that “This was the (summer?) residence of the continental governor, who at the time of the destruction of Atlantis was a woman.”(b) Others, such as Rand Flem-Ath along with the late Colin Wilson, as well as Jim Alison, have included the Andean site in proposed global grids linking prehistoric sites.
A less-known Inca site is that of Choquequirao(f), sometimes referred to as the ‘sister’ of Machu Picchu. Only a third of the site has been excavated so far.
Geodesy is usually defined as the measurement and mapping of the Earth. As a science, it is traced back to Pythagoras (6th cent. BC), who was thought to be the first to propose the sphericity of the Earth. Later, Eratosthenes (276 BC– 195 BC) was one of the earliest to attempt to determine the dimensions of our Earth and succeeded with remarkable accuracy.
A controversial aspect of modern geodesy is the claim that many ancient sites were deliberately established at locations that had a specific geodetic relationship to each other and/or the dimensions of the Earth. For example(a) in ancient Egypt, from Giza to the Equator is 1/12th the circumference of the Earth, Amarna to the Equator is 1/13th, Luxor 1/14th and Philae 1/15th! Graham Hancock in his Heaven’s Mirror pointed to similar relationships around the globe suggesting a possible world grid. This idea of a world grid has a number of supporters but is often classified as a ‘fringe’ interest due to the attempt by some to link gridlines with UFOs and their use of the grid as a power source(w).
Possibly related features may be the ley lines identified by Alfred Watkins in Britain(c)(g), the Alesia alignments in France discovered by Xavier Guichard(b) and/or the Heilige Linien of Germany claimed by Wilhelm Teudt(aa).
Heinz Kaminski had claimed to have discovered a megalithic grid system that stretched from Stonehenge across Europe with an east-west and north-south orientation and referred to as the Stonehenge/Wormbach System(h).
Even more exotic is the ancient Raetiastone navigation system rediscovered by Gerhard Pirchl (1942-2013) and outlined in a book by  Thomas Walli(ae).
Ashley Cowie has published a paper(ac) related to Alesia and the work of Guichard and others, as well as his own investigations.
I should also point out that Marcel Mestdagh also identified a form of a road system, laid out in giant ovals with radials in France. At the centre of these ovals was the ancient city of Sens. Philip Coppens informs us [1275.184] that a further strange discovery by Mestdagh was that this ancient road network, centred on Sens, was mirrored by a similar network of roads in England centred on Nottingham!
‘The Way of Virachoca’ in the Andes which runs through Tiwanaku and is oriented exactly 45° west of true north and runs for over 1000 miles, has been studied by Maria Scholten d’Ebneth  in the 1970s and expanded on by a number of Spanish speaking commentators and is now the subject of an article by Dave Truman(x).
In 1973, three Russians, engineers Valery Makarov and Vyacheslav Morozov along with Nikolay Goncharov, an artist, published in Russian an article with the eye-catching title of Is the Earth a Giant Crystal? (y) This was probably the earliest presentation of an earth grid based on ancient historical sites. A brief history of the earth grid theories that emerged around this time is available online(z). There is now a Russian geodesy website with an English translation(ab).
David Hatcher Childress published his Anti-Gravity and the World Grid  in 1993, with the modest claim that he “proves that the earth is surrounded by an intricate electronic grid network offering free energy.” Obviously, Childress’ understanding of ‘proof’ is different to mine, as the only proof required is the production of some of this free energy, which he has not done.
Tom Brooks has entered the fray with a study of 1500 prehistoric sites and his conclusion that the inhabitants of ancient Britain had a designed a navigation system based on a grid of isosceles triangles(i). Brooks has gone a step further and speculatively claimed that the accuracy of this geometry-based system could only have been designed through “extraterrestrial intervention”(r). This concept is explored more fully in his latest book, Seeing Around Corners: Geometry in Stone Age Britain  and in a series of video clips(s). A more critical view of Brooks’ ideas is also available on the Internet(j).
Some years ago a former employee of a NASA sub-contractor, Maurice Chatelain claimed that within a 450-mile radius of the Aegean island of Delos that 13 mystical sites, when connected by straight lines formed a perfect Maltese Cross(u)!
Others such as Livio Stecchini(d) and Jim Alison(e) using geodetic calculations have identified São Tomé and Cape Verde respectively as the location of Atlantis. I must also include Hugo Kennes, a Belgian researcher with a passionate interest in global grids and sacred geometry(l). Kennes has also informed me of a new Facebook group(q) deal with all aspects of the subject, as well as another(v) that includes submerged cities and other features.
Anyone interested in pursuing a study of this subject might like to look over James Q. Jacobs’ archaeogeodesy website(f) as well as the BioGeometry website (m).
If you have pursued all the links so far, you can pamper yourself further with a paper(k) by William Becker and Beth Hagens(n). Another researcher in this field is Dan Shaw whose website(o) gives a good overview of the subject.
Jean-Pierre Lacroix added his weight to the debate with his 1998 paper entitled The Mapmakers from the Ice Age(t).
A global network of sacred sites was also put forward by Rand Flem-Ath & Colin Wilson in The Atlantis Blueprint . This book was intended as a sequel to When the Sky Fell , but generally wandered off into other areas after the first couple of chapters.
I am somewhat sceptical about certain aspects of geodesy, particularly some of the claims of a world grid. However, it does raise many questions that require further study and explanation. In this connection, I would recommend John Sase’s Curious Alignments  as a good starting point. He confirms the work of Guichard and also offers a range of his own discoveries in the Great Lakes region.
In February 2020, Frank Maglione Nicholson, Ken Phungrasamee & David Grimason, collectively known as The Nazca Group(ad), published The Nazca Great Circle Map Hypothesis. Their claim is that “The lines and geoglyphs carved into the Nazca plateau represent a map of the Earth. The map is a Great Circle Map: a gnomonic projection with the center of the Earth as its cartographic view point. Each line on the Nazca Plateau represents a great circle of navigation centered at the center of the Earth and encircling the entire planet. The majority of the lines on the Nazca Plateau radiate from five loci of origin called radial centers.” I found this rather esoteric proposition difficult to absorb.
>Arturo Villamarin has published many books  and papers(af)(ag) in which the geometry and astronomy of archaeological monuments; Göbekli Tepe, Stonehenge, Teotihuacán and Mohenjo Daro, among others, are discussed.<
(d) http://www.metrum.org/mapping/atlantis.htm (link broken Dec. 2020)
(r) https://www.prehistoric-geometry.co.uk/ [See (i)]
Jim Alison has written an extensive paper(a) on the highly controversial subject of a global aligment of ancient sites such as the Great Pyramid, Easter Island and Machu Picchu(b). At the end of the first page he concludes that the Cape Verde islands are possibly the remnants of Plato’s Atlantis, based on the geodetic fact that “Machu Picchu and the Great Pyramid are equally distant from the Cape Verde Islands. Easter Island and the Indus Valley are also equally distant from Cape Verde.” For similar reasons he thinks that the Bay of Bengal as well as near Ilha Martin Vaz, a location off the coast of Brazil, should also be considered as possible candidates.