Stonehenge is perhaps the world’s most famous prehistoric monument. It was built in several stages: the first monument was an early henge monument, built about 5,000 years ago, and the unique stone circle was erected in the late Neolithic period about 2500 BC. In the early Bronze Age many burial mounds were built nearby. Today, along with Avebury, it forms the heart of a World Heritage Site, with a unique concentration of prehistoric monuments.
The First Stage
The first Stonehenge was a large earthwork or Henge, comprising a ditch, bank, and the Aubrey holes, all probably built around 3100 BC. The Aubrey holes are round pits in the chalk, about one metre wide and deep, with steep sides and flat bottoms. They form a circle about 284 feet in diameter. Excavations have revealed cremated human bones in some of the chalk filling, but the holes themselves were probably made, not for the purpose of graves, but as part of the religious ceremony. Shortly after this stage Stonehenge was abandoned, left untouched for over 1000 years.
The Second Stage
The Arrival of the Bluestones
The second and most dramatic stage of Stonehenge started around 2150 BC. Some 82 bluestones from the Preseli mountains, in south-west Wales were transported to the site. It is thought these stones, some weighing 4 tonnes each were dragged on rollers and sledges to the headwaters on Milford Haven and then loaded onto rafts. They were carried by water along the south coast of Wales and up the rivers Avon and Frome, before being dragged overland again to near Warminster in Wiltshire. The final stage of the journey was mainly by water, down the river Wylye to Salisbury, then the Salisbury Avon to west Amesbury.
This astonishing journey covers nearly 240 miles. Once at the site, these stones were set up in the centre to form an incomplete double circle. ( During the same period the original entrance of the circular earthwork was widened and a pair of Heel Stones were erected. Also the nearer part of the Avenue was built, aligned with the midsummer sunrise.)
The third stage of Stonehenge, about 2000 BC, saw the arrival of the Sarsen stones, which were almost certainly brought from the Marlborough Downs near Avebury, in north Wiltshire, about 25 miles north of Stonehenge. The largest of the Sarsen stones transported to Stonehenge weigh 50 tonnes and transportation by water would have been impossible, the stones could only have been moved using sledges and ropes. Modern calculations show that it would have taken 500 men using leather ropes to pull one stone, with an extra 100 men needed to lay the huge rollers in front of the sledge.
These were arranged in an outer circle with a continuous run of lintels. Inside the circle, five trilithons were placed in a horseshoe arrangement, whose remains we can still see today.
The Final Stage
The final stage took place soon after 1500 BC when the bluestones were rearranged in the horseshoe and circle that we see today. The original number of stones in the bluestone circle was probably around 60, these have long since been removed or broken up. Some remain only as stumps below ground level.
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Thousands of years ago, an ancient civilization raised a circle of huge, roughly rectangular stones in a field in what is now Wiltshire, England. Stonehenge, as it would come to be called, has been a mystery ever since.
Building began on the site around 3100 B.C. and continued in phases up until about 1600 B.C. The people who constructed the site left no written records and few clues as to why they bothered to schlep the stones to this spot.
Wild theories about Stonehenge have persisted since the Middle Ages, with 12th-century myths crediting the wizard Merlin with constructing the site. More recently, UFO believers have spun theories about ancient aliens and spacecraft landing pads.
But Stonehenge has inspired a fair number of scientifically reasonable theories as well. Here are five major (and not necessarily mutually exclusive) reasons Stonehenge might exist. [Gallery: Stunning Photos of Stonehenge]
1. A place for burial
Stonehenge may have originally been a cemetery for the elite, according to a new study. Bone fragments were first exhumed from the Stonehenge site more than a century ago, but archaeologists at the time thought the remains were unimportant and reburied them. Now, British researchers have re-exhumed more than 50,000 cremated bone fragments from where they were discarded, representing 63 separate individuals, from Stonehenge. Their analysis, presented on a BBC 4 documentary on March 10, reveals that the people buried at the site were men and women in equal proportions, with some children as well.
The burials occurred in about 3000 B.C., according to study researcher Mike Parker Pearson of the University College London Institute of Archaeology, and the very first stones were brought from Wales at that time to mark the graves. The archaeologists also found a mace head and a bowl possibly used to burn incense, suggesting the people buried in the graves may have been religious or political elite, according to The Guardian newspaper.
2. A place for healing
Another theory suggests that Stone Age people saw Stonehenge as a place with healing properties. In 2008, archaeologists Geoggrey Wainwright and Timothy Darvill reported that a large number of skeletons recovered from around Stonehenge showed signs of illness or injury. The archaeologists also reported discovering fragments of the Stonehenge bluestones — the first stones erected at the site — that had been chipped away by ancient people, perhaps to use as talismans for protective or healing purposes.
3. A soundscape
Or perhaps Stonehenge's circular construction was created to mimic a sound illusion. That's the theory of Steven Waller, a researcher in archaeoacoustics. Waller says that if two pipers were to play their instruments in a field, a listener would notice a strange effect. In certain spots, the sound waves from the dual pipes would cancel each other out, creating quiet spots.
The stones of Stonehenge create a similar effect, except with stones, rather than competing sound waves, blocking sound, Waller reported in 2012 at the annual meeting of the American Association for the Advancement of Science. Legends associated with Stonehenge also reference pipers, Waller said, and prehistoric circles are traditionally known as "piper stones."
Waller's theory is speculative, but other researchers have confirmed that Stonehenge had amazing acoustics. A study released in May 2012 found that the circle would have caused sound reverberations similar to those in a modern-day cathedral or concert hall.
4. A celestial observatory
No matter why it was built, Stonehenge may have been constructed with the sun in mind. One avenue connecting the monument with the nearby River Aven aligns with the sun on the winter solstice; archaeological evidence reveals that pigs were slaughtered at Stonehenge in December and January, suggesting possible celebrations or rituals at the monument around the winter solstice. The site also faces the summer solstice sunrise, and both summer and winter solstices are still celebrated there today. [Gallery: Stunning Summer Solstice Photos]
5. A team-building exercise
Or perhaps Stonehenge was something like an ancient team-building exercise. According to the University College London's Pearson, the beginning of the site's construction coincides with a time of increased unity among the Neolithic people of Britain. Perhaps inspired by the natural flow of the landscape, which seems to connect summer solstice sunrise and winter solstice sunset, these ancient people may have banded together to build the monument, Pearson suggested in June 2012.
"Stonehenge itself was a massive undertaking, requiring the labor of thousands to move stones from as far away as west Wales, shaping them and erecting them," he said in a statement. "Just the work itself, requiring everything literally to pull together, would have been an act of unification."