Scientists think they know why Stonehenge was rebuilt thousands of years ago

By Ashley Strickland, CNN

(CNN) — Scientists made a major discovery this year linked to Stonehenge — one of humanity’s biggest mysteries — and the revelations keep coming.

A team of researchers shared evidence in August suggesting that the Altar Stone, an iconic monolith at the heart of Stonehenge, was transported hundreds of miles to the site in southern England nearly 5,000 years ago from what’s now northeastern Scotland. Just a month later, a report led by the same experts ruled out the possibility that the stone came from Orkney, an archipelago off Scotland’s northeastern coast that’s home to Neolithic sites from that time frame, and the search for the monolith’s point of origin continues.

Now, research building on the two previous studies suggests that Stonehenge may have been reconstructed in England around 2620 to 2480 BC to help unify ancient Britons as newcomers arrived from Europe. The new study, published Thursday in the journal Archaeology International, also reveals how Neolithic people may have moved the 13,227-pound (6-metric-ton) block over 435 miles (700 kilometers) from where it originated.

Similarities between stone circles in Scotland and Stonehenge, located in Wiltshire on the southern edge of England’s Salisbury Plain, add to a growing collection of clues showing there was likely more connectivity between ancient societies in these two distant areas than once thought, according to the study.

Together, the findings from the new study and those published earlier this year are shedding light on the purpose of Stonehenge and the arrangement of its monoliths, an enduring enigma since excavations began at the site in the 17th century.

“These new insights have significantly expanded our understanding as to what the original purpose of Stonehenge might have been,” said lead study author Mike Parker Pearson, professor of British later prehistory at the University College London’s Institute of Archaeology, in an email. “It shows that this site on Sailsbury Plain was important to the people not just living nearby, but across Britain, so much so that they brought massive monoliths across sometimes hundreds of miles to this one location.”

A mysterious monument

Construction on Stonehenge began as early as 3000 BC and occurred over several phases in an area first inhabited as early as 5,000 to 6,000 years ago, according to the researchers.

Previous analysis has shown that bluestones, a type of fine-grained sandstone, and larger silicified sandstone blocks called sarsens were used in the monument’s construction. The bluestones were brought from 140 miles (225 kilometers) away at the Preseli Hills area in west Wales and are thought to have been the first stones placed at the site. The sarsens, used later, came from the West Woods near Marlborough, located about 15 miles (25 kilometers) away.

Researchers believe the Altar Stone was placed within the central horseshoe during a rebuilding phase. While the exact date is unknown, the study authors believe the stone arrived between 2500 and 2020 BC.

It’s during that rebuilding phase, according to the research, that Stonehenge’s builders erected the large sarsen stones to form an outer circle and an inner horseshoe made of trilithons, or paired upright stones connected by horizontal stone beams, which remain part of the monument to this day.

The Altar Stone is the largest of the bluestones used to build Stonehenge. Today, the Altar Stone lies recumbent at the foot of the largest trilithon and is barely visible peeking through the grass.

Many questions remain about the exact purpose for Stonehenge and the Altar Stone. But the monument aligns with the sun during the winter and summer solstices.

“There’s good evidence to suggest that these large stone monoliths have ancestral significance, representing and even embodying the ancestors of the people who placed them,” Parker Pearson said. “(The Altar Stone’s) location within Stonehenge is important as if you stand at the center of the stone circle, the midwinter solstice sun sets over its middle.”

During the winter, Neolithic people would gather near Stonehenge at the village of Durrington Walls, bringing pigs and cattle with them for a feast, Parker Pearson said. Stonehenge was also the largest burial ground of its time, lending support to the idea that the site may have been used as a religious temple, a solar calendar and an ancient observatory all in one.

And nearly half the Neolithic people buried near Stonehenge came from somewhere other than Salisbury Plain.

The new research adds a political twist to the backstory of a rebuilt Stonehenge.

“The fact that all of its stones originated from distant regions, making it unique among over 900 stone circles in Britain, suggests that the stone circle may have had a political as well as a religious purpose — as a monument of unification for the peoples of Britain, celebrating their eternal links with their ancestors and the cosmos,” Parker Pearson said.

Bridging distant communities

This show of unity — transporting giant stones long distances — would not have been easy for Neolithic people. The study authors don’t think boats at the time would have been strong enough to carry anything like the Altar Stone across coastal waters.

“Though the wheel had been invented elsewhere, it hadn’t quite reached Britain yet, so the massive stone blocks would likely have had to be dragged by wooden sledge sliding atop wooden rails that could be continuously lifted and re-laid,” Parker Pearson said.

The wooden sledge could have had shock absorbers made from vegetation to cushion the stone, which would have been susceptible to cracking on the long journey, the study authors said.

Hundreds, and possibly thousands, of people would have been needed to help move the stone over land, and the journey may have taken about eight months, the researchers noted in the paper.

“Travel by land would have provided much better opportunities for spectacle, pageantry, feasting and celebration that would have drawn people in (the) thousands to witness and take part in this extraordinary venture,” according to the study.

Moving the massive stone from Scotland to southern England suggests there was a network between two distant groups fostered by collaboration and cooperation — something the researchers think existed due to striking cultural similarities in both locations.

“They would have taken significant coordination across Britain — people were literally pulling together — in a time before telephones and email to organize such an effort,” Parker Pearson said.

The Altar Stone is similar in both size and placement to other large horizontal blocks in stone circles found in northeast Scotland, the study authors said. These recumbent stone circles have only been found in that part of Scotland, rather than the rest of England, which suggests that the Altar Stone may have been a gift from the community in northern Scotland to signify a type of alliance.

“Moreover, if you look at the layouts of some of the houses at Durrington Walls near Stonehenge, there’s a striking similarity in their architecture to those found far north in the Orkney Islands, but rarely anywhere in between,” Parker Pearson said. “We’ve also known for some time that people shared a style of pottery — which we call Grooved Ware — across the entire island of Britain. It seems to have been one of several innovations that were developed in Scotland and spread south from 3000 BC onwards.”

Unifying a decreasing population

As an island, Britain’s population has changed multiple times. The region’s early farmers descended from people from the Middle East who arrived on the island about 6,000 years ago, bringing agricultural practices with them. The newcomers replaced hunter-gatherer communities that had inhabited Britain previously and formed the majority of the population from 4000 to 2500 BC, Parker Pearson said.

But around 2500 BC, people began to arrive in Britain from Europe, largely from what’s now known as Germany and the Netherlands, and it’s around this time when Stonehenge was rebuilt, according to the study.

The researchers believe that the rebuilding process was “a response to a legitimation crisis brought on by this influx of new people” and an attempt to unite the Neolithic farmer population.

The European arrivals, called the Beaker people for the distinctive pottery that they buried with their dead, brought technology such as the wheel and metalworking with them.

“Within 16 generations over 400 years it seems that most people had ancestries that were a mix of the two, yet this was a mix of 90% incomer to 10% indigenous farmer,” Parker Pearson said. “The genetic makeup of Britain’s population almost completely changed over half a millennium.”

Eventually, the Beaker people’s descendants replaced Neolithic farmers and became Britain’s dominant population. So ultimately, Stonehenge, which brought “together these extraordinary and alien rocks which (symbolized) and embodied far and distant communities within a complex material and monumental expression of unity between people, land, ancestors and the heavens,” failed to unify the same communities which built it, the study authors noted.

“The findings of this study shed most unexpected and highly impressive new light on the history of Stonehenge – a remarkable achievement considering how well-studied this famous site has been,” said Duncan Garrow, a professor in the department of archaeology at the University of Reading specializing in European prehistory. Garrow was not involved in the new study.

Now, the researchers are redoubling their efforts to determine where exactly in northeast Scotland the Altar Stone originated, said Richard Bevins, coauthor of the new study, as well as the previous studies this year concerning the Altar Stone. Bevins is an honorary professor in the department of geography and Earth sciences at the UK’s Aberystwyth University.

“It’s really gratifying that our geological investigations can contribute to the archaeological research and the unfolding story as our knowledge has been improving so dramatically in just the last few years,” Bevins said. “Our research is like forensic science. We are a small team of (Earth) scientists, each bringing their own area of expertise; it is this combination of skills that has allowed us to identify the sources of the bluestones, and now the Altar Stone.”

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