Almost 5,000 years ago people came from all over Britain to feasts held near the great stone constructions at Stonehenge and Avebury. As if such journeys were not hard enough on foot over muddy tracks, many went to the trouble of bringing pigs.

Pig bones have been excavated and dated from four sites, Durrington Walls near Stonehenge, Marden and West Kennet Palisade Enclosures, both near Avebury, and Mount Pleasant close to the southern coast, revealing great feasts took place there during the Late Neolithic. Dr Richard Madgwick of Cardiff University studied the isotopes in the bones from 131 pigs buried between 2,800-2,400 BCE and found many were not local.

As shown below, the isotope strontium-87 is more common, relative to strontium-86, in the Scottish Highlands and Wales than it is in south-central England. Animals incorporate these ratios into their bones, based on what they eat, which in turn reflects the ground in which their food supply grew. A pig whose bones have a 0.712 ⁸⁷Sr/⁸⁶Sr ratio might come from many places, none near Stonehenge.

Less than a quarter of the pigs at each site were raised locally, and the West Kennet pigs were all from more than 50 kilometers (30 miles) away, probably much further.

The bones' isotopic signatures indicated the places the pigs came from were not only distant from where they were buried, but far from each other – a single herd of pigs was not driven from the same place as a lone act of tribute.

Madgwick was unable to match the fingerprint of isotopic ratios for strontium, sulfur, oxygen, carbon, and nitrogen to specific locations. For some elements the variation is less by region than by ecosystem – woodland acorns have different carbon ratios from field crops, for example. Moreover, the distribution of sulfur isotopes across Britain has not been well mapped, and Madgwick's work is hampered until this changes.

Nevertheless, at least five of the pigs appear to have originated from Scotland, and others probably came from at least as far as Wales. Some pigs had sulfur isotopes, indicating they originated in coastal locations.

“Transporting pigs over even modest distances across the Neolithic landscape would have required considerable effort,” Madgwick notes in Science Advances. Unlike sheep and cattle, there is little evidence of it happening elsewhere in the ancient world.

Since pigs could have been bought locally and donated to a feast, there must have been cultural pressure to bring from home.

"These gatherings could be seen as the first united cultural events of our island, with people from all corners of Britain descending on the areas around Stonehenge to feast on food that had been specially reared and transported from their homes," Madgwick said in a statement.