New chemical analysis of cremated remains unearthed at Stonehenge suggests that several of the people buried there came from farther west, possibly even from the same area of Wales as the “bluestones,” the shorter, bluish-gray stones that form the inner ring of the monument.

Over the last century, archaeologists have pored over the details of Stonehenge’s construction, but they’ve largely ignored the 58 people interred in a ring of 56 shallow pits, now called Aubrey holes, around the monument. Until recently, the cremated remains of these ancient Britons didn’t have much to tell archaeologists, because the heat of cremation tends to destroy most of the evidence about where people came from and how they lived.

But strontium turns out to withstand the heat, and it’s giving archaeologists new clues about where the people buried at Stonehenge spent the last few years of their lives.

Relatively light elements like carbon and oxygen are altered by the high temperatures, changing the isotopic ratios that give archaeologists information about a bone's history, but strontium is a heavier element and isn't changed by the heat. “Thanks to the high temperatures reached, the structure of the bone is modified, making the bone resistant to post-mortem exchanges with burial soil,” lead author Christophe Snoeck, a geochemist and archaeologist at Vrije Universiteit Brussel, told Ars.

Life stories written in bone

Different types of bedrock have different ratios of isotopes of the element strontium. Strontium-87 is the radioactive decay product of rubidium-87, so a rock’s ratio of strontium-87 to strontium-86 depends on its starting amounts of both isotopes, its initial levels of rubidium-87, and its age. As the strontium in the bedrock dissolves, plants take it up through their roots. When animals (including us) eat plants, we ingest the strontium, which replaces some of the calcium in our bones. So the ratio of strontium isotopes in your bones can be traced to the area of bedrock where your food was grown (modern food supply systems are really going to confuse future archaeologists).

In tooth enamel, which is where archaeologists usually get their strontium samples, those ratios usually reflect the plants a person ate during childhood, when the teeth were forming. But in bone, they reflect the plants a person ate for about the last ten years of life.

On the Wessex chalk underlying Stonehenge and the rest of the Salisbury Plain, the strontium isotope ratios usually fall between 0.7074 and 0.7090. But 125 miles (200km) to the west, across an expanse of western Britain that includes southwestern Wales, those values are much higher, in the neighborhood of 0.7110.

So Snoeck and his colleagues took samples from skull fragments of 25 individuals. Based on other bone fragments, six of those individuals were probably female, nine were probably male, and the sex of the other 10 couldn’t be determined. Three of the 25 were juveniles, and the other 22 were adults.

Local flavor

Most of the strontium isotope ratios fell within the bounds of the Wessex chalk where Stonehenge stands, meaning that these 15 people spent the last decade or so of their lives eating food grown within about 9.3 miles (15km) of the monument. But 10 of the people sampled had higher ratios, suggesting that their diets in their final decade were grown in soils well to the west of Stonehenge. Several of them had strontium isotope ratios that fell somewhere in between those for the Wessex chalk and those of western Britain, so they might have lived only a few miles away, but others’ ratios were high enough to suggest that they’d almost certainly spent time much farther west, more than a hundred miles away, and somehow come to be interred at Stonehenge.

But that story may not be as simple as it looks. Strontium isotope ratios in bone only record a person’s diet for about the last ten years of life, so that’s all the data can tell us. The people who spent their final years in West Britain may have lived their whole lives there and then either moved to the area around Stonehenge or been brought there for burial, but it’s also possible they lived in Wessex, or somewhere else entirely, earlier in life. Those with ratios somewhere in the middle range may have lived and died a few tens of miles northwest of Stonehenge, or those ratios may reflect a mixture of time spent in West Britain and in Wessex, perhaps moving back and forth. There’s a lot of complexity in people’s life histories that we just can’t see in the snapshot the strontium isotope analysis provides.

But it’s clear that not everyone who was buried at Stonehenge lived nearby for their entire lives, and some of them may even have died far away from the monument at which they were laid to rest.

“It shows that being chosen to be buried at Stonehenge was not only limited to those living at/near Stonehenge and thus, the site was not used only by a ‘local community,’” Snoeck told Ars. And it suggests that people, as well as building materials, were moving around Britain regularly as early as 5,000 years ago, and those movements created social, spiritual, and apparently personal connections between regions.

A final journey

And there’s some evidence in favor of the idea that, whatever their life history, the people interred at Stonehenge made the trip posthumously after being cremated back home.

Cremation, as Snoeck said, usually wipes out the carbon-13 ratios in bone, which would otherwise provide information about the person’s diet. Instead, the carbon-13 ratios in cremated bone usually reflect those in the wood used for the funeral pyre—which usually depend on how much light the trees received while they were growing. Trees from a relatively open landscape, like the chalk downlands near Stonehenge, usually have higher carbon-13 values than those grown in denser woods, like those in southwest Wales. And the bones of the people buried at Stonehenge had a wide range of carbon-13 values.

Their cremations, Snoeck and his colleagues say, probably happened under different conditions, using different types of wood as fuel, and it seems likely that they happened in completely different places. Some of the people interred at Stonehenge may have died and been cremated in West Britain and then brought the 125 miles (200km) to Stonehenge for burial. That would match 1920s archaeologists’ reports that the remains looked as if they’d originally been placed into the Aubrey holes in leather bags, giving the impression that they’d “been brought from a distant place for interment.”

At the time, the site would be hard for modern visitors to recognize; the distinctive Sarsen stones wouldn't be erected until around 2000 BCE. Inside an earthen embankment, the Aubrey Holes formed a wide circle around a central open space. Wooden posts, or perhaps the bluestones, stood in most of the Aubrey Holes, perhaps marking the cremated remains buried there. Radiocarbon dates of the remains span centuries, from 3,180 BCE to 2,380 BCE, so we know the site served as a cemetery for nearly a thousand years—though clearly not just a local one.

But we still don’t know why ancient Britons would carry some of their dead such a long distance for burial or how they chose which of their dead to bury at Stonehenge. Snoeck and his colleagues suggest that the interments may have happened in conjunction with the transport and raising of the bluestones, which is an especially interesting idea given recent suggestions that the bluestones were first erected in the Aubrey holes and would have stood atop the cremated remains.

“Looking at the spread in the radiocarbon dates (covering several centuries), I don't think this was a single event,” Snoeck told Ars.

A Welsh connection?

We already know that the bluestones, a mixture of rhyolite and spotted dolerite, came from the Preseli Hills in Western Wales. In fact, for some of them, chemical analysis has narrowed down which quarries they came from: Craig Rhos-y-felin and Carn Goedog. And that region of Wales happens to fall within the area of Western Britain that matches the strontium isotope ratios in the bones at Stonehenge. But the isotope analysis alone can only point to a broad area that has similar geology. (In fact, it’s technically possible that those 10 non-local people buried at Stonehenge came from somewhere in Scotland, Ireland, or continental Europe; Snoeck and his colleagues just consider it much less likely thanks to the distance and/or water crossings involved.) So it’s impossible to say, based on the strontium data, that these people lived in Wales.

But since there’s already a connection with Western Wales, it’s not unreasonable to suggest that at least some of the people from Stonehenge came from the same place.

Nature Scientific Reports, 2018. DOI: 10.1038/s41598-018-28969-8 (About DOIs).