It's the most popular site to watch the sun rise on the summer solstice. Yet the latest research suggests that the ancient people who erected the massive stones, after hauling them 240km, were more interested in midwinter or even their healing properties, writes Robert Matthews
This week, crowds will gather at sites from New York to Norway to take part in one of the most ancient of all rituals: watching the sun rise on the summer solstice - the longest day of the year in the Northern Hemisphere.
The largest gathering will be at the most celebrated of these sites - Stonehenge, in Wiltshire, England. Each year, many thousands of people try to get close to the enigmatic stone circles in the (usually vain) hope of witnessing the rising of the solstice sun.
Yet new research suggests that this modern-day ritual has been misconceived, occurring at the wrong place at the wrong time - and with everyone looking in the wrong direction.
This is among a whole slew of insights emerging about Stonehenge following recent studies by archaeologists. Taken together, they point to a whole new conception of Stonehenge's origins, purpose and evolution.
What hasn't changed are the estimates of the astonishing antiquity of these sites. Dating of artefacts found around Stonehenge show that its construction began about 5,000 years ago.
To put that into context, when building began at the site, the Great Pyramids of Egypt were still 500 years in the future.
Most archaeologists agree that the first structures at the Wiltshire site took the form of a circular ditch with a bank - a "henge" - that had 56 pits, known as Aubrey Holes, arranged within it.
But while there is broad agreement on dates, archaeologists are now questioning the standard image of Stonehenge at these times. They believe that from the outset, the site featured "bluestones" made from a volcanic rock known as spotted dolerite.
And therein lies the first astonishing fact about Stonehenge. The source of these bluestones has been traced to an outcrop more than 240 kilometres away in the hills of Pembrokeshire, Wales. Exactly how scores of bluestones, some weighing more than four tonnes, were transported so far by Neolithic labourers has long been a mystery.
One theory is that nature did most of the heavy lifting during the last Ice Age, a glacier scooping up the rocks in Wales, and dumping them in central England when it melted about 10,000 years ago.
Recent research, however, has cast doubt on this. Analysis by researchers at the University of Wales has shown the bluestones were broken from their host outcrop and exposed to the air after the glaciers had vanished.
The idea that the stones were transported by human ingenuity has been revived following an experiment conducted in 2010 by Dr Andrew Young at the University of Exeter.
While working at a similar stone circle in Aberdeen, Scotland, archaeologists had found dozens of carved stone balls. Wondering if these might have acted as "ball bearings", Dr Young constructed a track capable of holding them in position as objects were rolled over them. Experiments showed that the technique allowed just half a dozen people to pull even the largest bluestones relatively easily.
But to what purpose - what was Stonehenge for? One of the most persistent theories is that it was some kind of giant astronomical observatory. More than 250 years ago, the English antiquarian William Stukeley pointed out that Stonehenge and the outlying "Heel Stone" - near which the sun will rise on Thursday - were orientated roughly towards the point of sunrise on the longest day of the year.
In the early 1960s, the astronomer Gerald Hawkins of Boston University made headlines with computer analysis that revealed what he claimed were a host of other alignments within the structure of Stonehenge, some of which could be used to predict eclipses of the Sun and the Moon.
Other academics, including the renowned Cambridge astrophysicist Prof Sir Fred Hoyle, made similar claims.
But many of these "alignments" have since been found to rely on imprecise measurements, and seem to be the result of coincidence or wishful thinking.
Now even the link with the summer solstice has come under suspicion. Two other major neolithic structures built around the time of the original Stonehenge - Maes- howe in Orkney and Newgrange in Ireland - have stone chambers clearly constructed to allow the Sun's light to enter them just once a year. And it is not on the summer solstice but its counterpart - Midwinter's Day.
This has prompted suspicions that the traditional view of Stonehenge is out by 180 degrees, the ancient monument having been originally designed for a ceremony taking place on the longest night of the year. The geometry of the giant blocks at the centre of Stonehenge shows that they could have acted as "windows" framing both the Sun and the Moon as they crossed the winter sky. On the shortest day, the setting sun would have shone through the stones, presaging the longest night.
Its significance remains unclear, but one suggestion, by the anthropologist Dr Lionel Sims of the University of East London, is that it may have been linked to ancestor worship, via the myriad stars visible for the longest time on Midwinter's Night. Intriguing support for this comes from the bluestones themselves - whose flecks of white quartz are reminiscent of stars in the night sky.
Recent excavations support the idea that Stonehenge was originally some kind of cemetery. Analysis of the enigmatic Aubrey Holes that surround the monument have revealed the presence of burnt human bone dating back 5,000 years, just when the monument was taking shape.
But a rival theory is emerging, based on the fact that many of the human remains found at Stonehenge show signs of skeletal trauma. This suggests the site was of significance for those with serious injury. Significantly, there has long been folklore ascribing healing powers to bluestones, and these tales are centred on both Wiltshire - where Stonehenge is located - and Pembrokeshire, the original site of the bluestones.
So was Stonehenge a place whose focus was on life or on death?
Archaeologists believe they may finally be closing in on the answer. But for most of those gathered around the site on Thursday, it is the sense of connection with antiquity that provides all the answers they want.
* Robert Matthews is visiting reader in science at Aston University, Birmingham, England
