For a set of craggy rocks in an English field, Stonehenge's ability to capture the imagination is impressive. The ancient monument composed of massive stones arranged into concentric circles by unknown builders is referenced almost as far back the Norman Conquest, when an English historian remarked in 1130 A.D. that "no one can conceive how such great stones have been so raised aloft, or why they were built here." That certainly hasn't kept many from trying. It seems like everyone has a theory for why the ruins were constructed. Some are more plausible than others.
With March 20 marking the vernal equinox (one of two days during the year where day and night are the same length) attention turns again to one of the more persistent theories for Stonehenge's origin. In a 1965 book, "Stonehenge Decoded," astronomer Gerald Hawkins offered the then-most comprehensive hypothesis to date of Stonehenge's purpose. Hawkins saw the cluster of stones, constructed in phases from around 3100 B.C. through 1600 B.C., as an ancient astronomical calendar. (See pictures of the seven wonders of the world.)
In his analysis, he identified 165 separate points on the monument, and linked them to astrological phenomenon like the two solstices and equinoxes and lunar and solar eclipses. It's a difficult theory to disprove completely and some evidence is persuasive at dawn on the summer solstice, for example, the center of the Stonehenge ring, two nearby stones (The Slaughter and Heel Stones) and the sun all seem to align. Still, critics of Hawkins' theory say he gives the ancient builders too much credit, arguing they wouldn't have had the sophistication or precision necessary to predict all the astrological events Hawkins' ascribes to his Stonehenge calendar. And plus this is England after all wet, overcast England. The climate may have prevented the ancient people of Stonehenge from even seeing the sky with regularity.
Still, Hawkins' theory is one of the more legitimate attempts at a Stonehenge explanation. In the 12th Century, the legend of King Arthur wasn't completely regarded as fiction. In his account of Stonehenge, historian Geoffrey of Monmouth wrote that troops tried to move the stones from Ireland to England in order to provide a monument for their war dead. When they couldn't, they enlisted the help of the wizard Merlin to transport the massive stones some weighing as much as 50 tons back to Britain before arranging them in the current configuration.
In a modern twist on Geoffrey's account, some argue that space aliens, rather than Merlin, constructed Stonehenge. These theories feed off the fact that no one's exactly sure how the rocks got to their present location the origin of some were traced as far as a Welsh mountain range 137 miles away from the Stonehenge. Although modern tests employing only technology from the era have moved similar stones, there's still no full explanation for how ancient people managed such a feat. Hence, aliens.
Some theories are even more inventive. In the 1920s, a Brit named Alfred Watkins attempted to connect Stonehenge with other sites in England, arguing that when taken together, they served as landmarks to navigate through the island once dense, now vanished, ancient forest. He called these routes "ley lines" and the theory developed a sizable following, though trained archaeologists were dubious about this amateur's theory. Another hypothesis is that the configuration is meant to resemble a giant vulva, as a means of tribute to an ancient fertility god. Others argue that Stonehenge was a place of ancient healing, and archaeologists have discovered skeletons at the site riddled with crude wounds, perhaps indications of rudimentary surgery.
The current consensus (if such a thing even exists) is that Stonehenge was used as a burial site. Archaeologists have found skeletal remains at the site dated to a 500-year period beginning in 3000 B.C. One dubbed the site a "domain of the dead" and say the bodies found likely belong to a select group of elite ancient people. It's the most solid evidence yet, but it doesn't preclude Stonehenge having a dual purpose as an astrological calendar or as a religious site. The only thing certain is that as the sun rises and sets to mark another equinox, another day will pass with the complete answer of the site's origins still firmly lodged in the past. Perhaps that's how it's meant to be.