The monument was built during a period of immigration from continental Europe and was likely intended to unite communities in the British Isles.

              Stonehenge is located on Salisbury Plain in southern England.                                    garethwiscombe via Wikimedia Commons under CC BY 2.0

About 5,000 years ago, prehistoric people in what is now southern England began building the circular formation of massive standing, stacked stones known today as Stonehenge. The monument is made of rock transported from far and wide, an impressive feat of transportation for its Neolithic builders.

Recent research suggests that the 43 bluestones at Stonehenge came from about 140 miles (225 kilometers) away in west Wales, while the larger sarsen stones came from 15 miles (24 kilometers) further north. The structure's central altar stone, which weighs 13,200 pound, came not from Wales, but from Scotland, more than 400 miles away.

The Altar Stone (bottom) lies buried beneath two sarsen stones. Nick Pearce /                                          Aberystwyth University

Based on these findings, archaeologists are proposing a new theory about the porpuse of Stonehenge. According to a study published in the journal Archaeology International, the circle came to unite the ancient inhabitants of Britain.

"The fact that all the stones [at Stonehenge] come from remote areas, making it unique among the more than 900 stone circles in Britain, suggests that the stone circle may have had a political and religious purpose: as a monument to the unity of the peoples of Britain, celebrating their eternal connections with their ancestors and the cosmos," said lead author Mike Parker Pearson, an archaeologist at University College London, in a statement.

Stonehenge was built in several stages. A 2015 analysis by Parker Pearson showed that the bluestones were laid first, around 2900 BC, followed by the Sarsen stones around 2500 BC. Stonehenge then underwent a rebuilding phase, during which prehistoric people erected a large outer circle of sarsen stones and an inner ring of trilithons (pairs of vertical stones above a horizontal architrave). It was during this phase, between 2500 and 2020 BC, that the altar stone was placed within the monument's central horseshoe . 

Today, the altar stone lies flat and is partially hidden by a fallen rock. As Parker Pearson tells Esther Addley of the Guardian, people have long assumed that it once stood there, but then fell. But researchers know of several circular monuments in northeast Scotland that were deliberately placed. They assume that the builders of Stonehenge quarried the altar stone from a remote Scottish district.

“Given what we now know about its origins, it seems even more likely that it was deliberately placed as a recumbent stone,” says Parker Pearson. It is “very likely” that the altar stone is part of an ancient Scottish monument, he adds. “These stones are not just plucked from nowhere.”

Stonehenge's location, on the vast Salisbury Plain, must have been important to both the nearby inhabitants of the area and people across Britain, Parker Pearson tells CNN's Ashley Strickland. The plain was large enough that ancient people "transported huge monoliths hundreds of miles to this location."

The distant origin of the stones led Parker Pearson and his colleagues to believe that the second phase of Stonehenge’s construction was intended to unite Britain. This era was marked by the arrival of new immigrants from Europe, mainly from what is now the Netherlands and Germany. The builders of Stonehenge may have added elements to the Salisbury monument “to unite the indigenous Britons,” the statement said.

“There is definitely some kind of interaction – you could call it ‘first contact’ [with the immigrants],” Parker Pearson tells the Guardian. “That’s when Stonehenge is built, and I wonder if it’s that moment of contact that kind of serves as a catalyst for this really impressive second phase of Stonehenge.” It’s an attempt to assert unity, more likely to integrate the newcomers – or not.”

Moving such large and heavy stones would have been an “extraordinary undertaking” in Neolithic Britain, the statement said. Although the wheel was invented in Mesopotamia around the fifth millennium BC, the technology had not yet reached the British Isles. Thus, moving the parts of Stonehenge would have “required the efforts of hundreds, if not thousands, of people”, making each act a demonstration of unity in itself.

As for the exact origin of the altar stone, the researchers have narrowed down the possibilities somewhat: this fall, they concluded that the stone did not come from the Scottish archipelago of Orkney.“It is really rewarding that our geological research can contribute to archaeological research and the development of history because our understanding has improved dramatically in recent years,” says Richard Bevins, co-author of the study and an archaeologist at Aberystwyth University in Wales, in the press release.

Since researchers began excavating and studying Stonehenge in the 17th century, the structure’s function has been a mystery. Early scholars suggested that the monument was a temple, a calendar, or an observatory. Stonehenge is famous for its association with the sun and moon, and modern people gather at the site during the solstice to celebrate the longest and shortest days of the year. New research on the monument’s stones has expanded its potential cultural significance.

“I think we haven’t been looking at Stonehenge the right way,” Parker Pearson told the Guardian. As he says in his statement, “the similarities in terms of architecture and material culture between the Stonehenge site and northern Scotland now make more sense. […] These distant places had more in common than we had thought.”