The remnants of prehistoric monuments still dot the modern British landscape. Around 4,500 years ago, people gathered at these sites or in nearby communities for annual winter feasts where the main delicacy on the menu was pork. Chemical analysis of the pig bones left behind after feasts at four major henge sites in southern Britain reveals a surprisingly far-flung network of Neolithic travel.

This little piggy went to Stonehenge...

Mount Pleasant Henge is a stone circle about 70km (44 miles) southwest of Stonehenge, near the coast of the English Channel. West Kennet Palisaded Enclosures is a set of circular ditches and palisades near the famous stone circle at Avebury, about 39km (24 miles) north of Stonehenge, while Marden Henge, between Avebury and Stonehenge, is a 14-hectare site surrounded by ditches and embankments that once held its own circle of standing stones. Durrington Walls, a large settlement (which eventually built its own stone circle) just 3km (1.86 miles) northeast of Stonehenge, was closely linked with the iconic monument itself.

"Stonehenge is for the dead, Durrington Walls for the living: the place of the builders of Stonehenge and the places of Stonehenge's feasts," archaeologist Richard Madgwick of Cardiff University told Ars Technica. Archaeologists have unearthed the remains of ancient feasting at all four sites: broken ceramics, discarded stone tools, and the bones of butchered pigs. Those 4,500-year-old leftovers suggest that these sites were hubs linking a Neolithic social network that connected far-flung communities from Scotland to Wales.

Isotopes of different chemical elements, preserved in an animal's bones and teeth, can reveal something about the kinds of foods it ate, the kind of soil it grew in, and the origins of the water it drank. For instance, the ratio of strontium-87 to strontium-86 in a bone sample can tell you about the local geology. Oxygen isotope ratios suggest information about rainfall patterns, and the percentage of the isotope sulfur-34 tends to be higher near the coast.

If the pigs at a site had mostly come from the local area, you'd expect the isotope ratios in their bones to be pretty similar. For instance, pigs raised on the Wessex chalk around Avebury and Stonehenge should have a ratio of strontium-87 to strontium-86 between 0.7077 and 0.7087. And pigs raised near the three inland henges should have had sulfur isotope ratios less than 0.14.

Bringing home the bacon

But for every isotope ratio the researchers tested—carbon, nitrogen, oxygen, strontium, and sulfur—each group of pigs showed a surprising amount of variation. Several of the pigs at Durrington Walls, which stands 56km (34.8 miles) from the nearest coast, had sulfur isotope ratios that suggested they'd been raised closer to the sea. Even at West Kennet, 74km (45.98 miles) inland, nine pigs (over half the total) appeared to have come from a coastal area. Madgwick and his colleagues found strontium isotope ratios representing every major geological area in Britain, and oxygen and carbon isotope ratios were also all over the map, suggesting that the pigs who ended up at the four sites had been reared in diverse landscapes.

Those wide ranges suggested that the pigs for the great feasts had come from several areas, each with different soils, different plants to forage on, and different rainfall patterns. Many of the pigs may have traveled more than 50km away to reach their final resting places. Because pigs aren't prone to making cross-country trips on their own, the findings suggest that people were traveling from all across Britain to attend feasts at these henge sites. And that means Neolithic Britain may have been much more interconnected than archaeologists realized.

From Scotland to Wales

Tracing individual pigs to their pastures of origin is difficult, partly because the ratios of most isotopes across Britain haven't yet been mapped at a high-enough resolution, and multiple areas might share similar isotopic signatures.

"Isotope data are generally most useful for eliminating potential areas of origin rather than for pinpointing locations," Madgwick and his colleagues wrote. But a few examples do stand out, and they underscore how people and livestock converged from the far corners of Britain to take part in winter feasts (for various definitions of "taking part").

A few pigs have surprisingly high ratios of strontium-87; two from West Kennet and one from Marden match small pockets of western England and southern and western Wales—an area previously linked to Stonehenge as the source of the bluestones and the possible homeland of some of the people interred at the monument. Five other pigs' strontium ratios fall into a range that suggests they probably came from Scotland, the far northern end of the island.

It's been obvious for quite a while that sites like Stonehenge, Avebury, and Marden were important to people who lived in the surrounding region. But these findings suggest that these sites played a role in the lives of communities all across Britain.

Potluck on the hoof

The findings also suggest that actually bringing pigs to the feast was important to people in Neolithic Britain. Pigs were their most common domesticated livestock at the time; it would have been very easy to travel from, say, Plymouth to Avesbury and buy a few local pigs for the feast once you got there. And pigs aren't easy to move long distances, unlike cattle—there's a reason you don't hear about the pig drives of the Old West. Ancient people went to a lot of effort to move their pigs a long distance for these feasts, and there was no reason at all to do that unless it was important to show up with your contribution from home.

Much like the effort it took to move the bluestones from the Preseli Hills of Wales, the findings suggest that ancient Britain was more connected than archaeologists previously thought. Sites like the ones studied here were also viewed as worth a tremendous amount of investment, even to people who lived far away and may only have visited once a year, at most.

"I think these were major socio-political events—pan-British events for uniting a disparate populace and engaging them in big monument builds and big feasts," Madgwick told Ars Technica.

Like many discoveries in archaeology, though, this chemical analysis raises more questions than it answers. "I have the what and the where, but I really want the how," Madgwick told us. "How did they get animals (and people) to the south over such distances? What were the routeways, and how important was maritime and riverine movement?"

That will be the focus of future work, along with whether monuments in northern Britain and Ireland also drew people from far afield.

Science Advances, 2019. DOI: 10.1126/sciadv.aau6078; (About DOIs).