Question: What are the theories behind Stonehenge?
About the article "Stonehenge", section "Function and construction".

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The Preselis are dotted with prehistoric remains, including evidence of Neolithic settlement.
In 1923 the petrologist Herbert Henry Thomas identified that bluestone from the hills corresponded to that used to build the inner circle of Stonehenge, and more recent geologists have identified Carn Menyn (formerly called Carn Meini) as one of the bluestone sources.
Advanced details of the most recent contribution to the puzzle of the precise origin of the Stonehenge bluestones were published by the BBC in November 2013.
Others theorise that bluestone from the area was deposited close to Stonehenge by glaciation.
More detailed discussions on the bluestone topic can be found in the Stonehenge, Theories about Stonehenge and Carn Menyn articles. 
Stonehenge has been subjected to many theories about its origin, ranging from the academic worlds of archaeology to explanations from mythology and the paranormal. 
In 1957 Hawkins became professor of astronomy and chairman of the department at Boston University in the United States.
He wrote widely on numerous subjects, including tektites, meteors and the steady-state universe theory.
Hawkins applied the technological resources of the university to studying the astronomical alignments of ancient megalithic sites.
He fed the positions of standing stones and other features at Stonehenge into an early IBM 7090 computer and used the mainframe to model sun and moon movements.
In his 1965 book, "Stonehenge Decoded", Hawkins argued that the various features at the monument were arranged in such a way as to predict a variety of astronomical events.
By interpreting Stonehenge as a giant prehistoric observatory, Hawkins' work re-assessed what had previously been seen as a primitive temple.
The archaeological community was skeptical and his theories were criticized by such noted historians as Richard Atkinson, who denounced the book as being "...tendentious, arrogant, slipshod, and unconvincing".
It sold widely, however.
It was especially popular amongst the members of 1960s counter culture, who found that it followed a similar "wisdom of the ancients" line explored by Alexander Thom.
Hawkins' theories still inform popular opinion of Stonehenge although archaeologists are cautious to accept them.
Many scholars accept that the importance of astronomical alignment and large complexes being planned and constructed to fulfill cosmology has been demonstrated at other prehistoric sites, such as the Snake Mound and Cahokia in the United States.
Hawkins later examined the Nazca lines in Peru, and concluded there was not enough evidence to support an astronomical explanation for them.
He also studied the temple of Amun at Karnak.
He continued to study Stonehenge up until his death. 
"Stonehenge Apocalypse" follows the pattern of many movies containing archaeology and archaeologists.
It has elements of science, mystery, exoticism, and even a hint of romance.
In the end the lead male character, Jacob Glaser, makes the ultimate sacrifice for her.
Glaser is trying to stop the Stonehenge Apocalypse and also prevent power from falling into the wrong hands, particularly into the hands of an evil archaeologist who wants to save only a few and not the entire world.
Heroic characters are a common thread in many films, but especially in films dealing with archaeology.
These heroes are usually embraced by popular culture.
Although Glaser begins as an academic failure, by the end of the film his far-out theories are proven right and just what is needed to save mankind.
He certainly qualifies as a hero in the end.
"Stonehenge Apocalypse" shows how dangerous the past is.
Stonehenge has always been an archaeological site surrounded in mystery, and that undoubtedly enhanced its popularity.
It is no surprise to have such a popular and well-known prehistoric site as the centerpiece of a film with archaeological content.
In the film, this mysterious site releases dangerous energy into the world.
Despite an evil energy emanating from Stonehenge, the archaeologists and other scientists continue their work.
The military steps in and decides they will take control and destroy the site, though the other characters and the audience realize is naïve to think this dangerous past can be destroyed.
The military is proven wrong and Jacob Glaser’s special knowledge saves the day. 
British author John Michell wrote that Alfred Watkins' ley lines appeared to be in alignment with various traditional sacred sites around the country.
Michell wrote that "There is a curious symmetry about the positioning of the three Perpetual Choirs in Britain.
Stonehenge and Llantwit Major are equidistant from Glastonbury, some 38.9 miles away, and two straight lines drawn on the map from Glastonbury to the other two choirs form an angle of 144 degrees...
The axis of Glastonbury Abbey points toward Stonehenge, and there is some evidence that it was built on a stretch on ancient trackway which once ran between the two Choirs".
Michell created diagrams that illustrated correlations between the design of Stonehenge and astronomical proportions and relationships.
However, the Welsh Triads refer not to Stonehenge but to the village of Amesbury which is two miles from Stonehenge.