The mechanics of Stonehenge’s construction have baffled scholars for centuries. The megaliths that make up the prehistoric monument weigh between 2 and 30 tons and had to be moved as many as 150 miles to their current site. Proposed explanations for their transport include giant wicker baskets, oxen and wooden sledges.

A new analysis by researchers at England’s Newcastle University adds a twist to the most widely accepted of these theories, which holds that the stone was loaded onto sledges (also known as sleds or sleighs) that slid on log tracks. As archaeologist Lisa-Marie Shillito suggests in the journal Antiquity, lipid residue found in pottery at the nearby Durrington Walls site indicates ancient Britons may have relied on pig fat to grease this system of logs and sledges.

According to Science magazine’s Eva Frederick, archaeologists previously posited that the high concentrations of lard left in bucket-sized ceramic containers at the prehistoric village resulted from elaborate feasts hosted by Stonehenge’s builders. Shillito believes otherwise, arguing that the size and shape of the pottery make it better suited for storing animal fat than cooking and serving meals. Additionally, the archaeologist notes in a statement from Newcastle, “The animal bones that have been excavated at the site show that many of the pigs were ‘spit roasted’ rather than chopped up as you would expect if they were being cooked in the pots.”

The hypothesis points out the multifaceted nature of artifacts originally assumed to serve just one purpose. In an interview with Newsweek’s Hannah Osborne, Shillito expanded on this idea: “Cooking/food has usually been the default assumption in archaeology when analyzing pottery residues. It's the most obvious explanation and often correct, but sometimes things are a bit more complex.”

She continues, “In this case it could be a ‘dual purpose’—cooking and collecting the fat as a by-product. I had the idea as the amount of fat we found in these pots was unusually high, the only comparable examples being in oil lamps.”

As Osborne writes, Stonehenge was built using two kinds of rock: The larger boulders, called “sarsen,” stand upwards of 25 feet tall and weigh more than 30 tons each. They were transported to what is now Salisbury, England, from a site 18 miles north. The smaller “bluestones,” on the other hand, originated at Wales’ Preseli Hills, some 140 miles away from the monument.

In 2016, an archaeological experiment conducted by researchers at University College London found that it would have been surprisingly simple for ancient builders to mount bluestones onto sycamore sleighs and pull them along on a track made out of logs. According to the Telegraph’s Sarah Knapton, ten volunteers managed to drag a one-ton stone at a rate of ten feet every five seconds, or more than one mile per hour if pulled at constant speed. Given the fact that the bluestones weigh between one and four tons, it’s plausible that groups of 20 could have hauled the rocks from Preseli to Salisbury with relatively little effort.

The new research supports a “greased sled” hypothesis, Shillito writes, pointing toward lard’s use as a friction-reducing lubricant designed to facilitate megalith transport. “There is so much evidence” showing how Stonehenge could have been built, Shillito tells Newsweek. “[We have] live modern experiments, ethnographic examples of people moving megaliths, and now … evidence for the lubricant that would have been used in the Neolithic. The only thing we don't have is the sleeper and sledges being preserved—as these would have been wood, which doesn't preserve [under] normal conditions."