Roman-era mixers and grinders made with geology in mind

AUSTIN, Texas – A study of stone tools from a Roman Empire outpost revealed that for ancient bakers and millers, having the right tools was all about geology.

A team of geoscientists and archaeologists made the discovery while analyzing tool samples in a geology lab at the University of Texas at Austin, discovering that the paste mixing vats and mills from the Roman ruins of Volubilis, a city in Morocco, were made from specific types of rocks which probably improved the function of each tool.

Additionally, researchers determined that the stones came from the region, a finding that challenges the theory that some grindstones were imported from afar. It also means that the artisans who made the tools may have received information directly from the workers who used them.

“It’s interesting because it’s a very local source and apparently a single source,” said Jared Benton, co-author of the study and an assistant professor at Old Dominion University who studies business. between the workshops of the Roman era. “You wonder if there isn’t a bunch of bakers who get together and say let’s buy our stuff from this one quarry, or maybe there’s just a guy who [sells the stones], and that’s all.”

The results were published in the Journal of Archaeological Science: Reports.

Derek Weller, a postdoctoral researcher at the Earthquake Research Institute at the University of Tokyo, led the study. Additional co-authors include Omero “Phil” Orlandini, research associate and director of the electron microbeam lab at UT Jackson School of Geosciences; Lauren LoBue and Scott Culotta, both students at Jackson School; and Christy Schirmer, a graduate student in the Classics Department at UT.

The study began in early 2020, when Schirmer showed up at Orlandini’s lab with a box of stones. These were pieces of stone tools that she and Benton had salvaged from the tools of Volubilis – and they were curious about where learning more about their geological makeup might take them.

“They kind of look the same when in tool form, but as soon as we started looking it was clear that they were completely different,” Orlandini said.

Olandini put LoBue and Culotta on the case. Undergraduates subjected all 16 samples to a detailed scientific examination to determine their geochemical composition.

Their research revealed a type of rock for each type of tool. Grain wheels were made from vesicular basalts (a volcanic stone full of sharp pores); oil mills were made from fossiliferous clastic limestone (a limestone containing fragments of other rocks and small fossil shells); and the kneaders were made from limestone without any clastic or fossil material.

The study notes how the attributes of rocks relate to the function of each tool. For example, the pores in the basalt may have helped provide cool edges that could help grind the wheat into flour when the stone was worn out.

Weller also used the geochemical data to determine that all of the stones were from sources close to Volubilis. Limestone is abundant in the region, and two limestone quarries were already known to be active in Roman times near Volubilis. But archaeologists previously believed that the basalt – which Weller discovered came from the nearby Middle Atlas mountains – was imported from Italy.

Additionally, research revealed that each type of rock came from a single location rather than different locations around Volubilis. Benton said this suggests that a single supplier for each type of stone could have met all of the town’s demand and gained input from locals.

Elizabeth Fentress, an archaeologist specializing in Roman settlements in North Africa, said the study is a great example of collaborative research.

“This is not the only collaboration between geologists and archaeologists, but an excellent collaboration,” she said. “The key is, like here, that archaeologists ask the right questions and use their knowledge to interpret the answers. “