Mass production over 1800 years ago: The Roman mill complex at Barbegal in what is now southern France is considered to be one of the oldest industrial production facilities in history. Scientists have now gained new insights into the hydraulic technology that once set the 16 mill wheels in motion: Unusually elbow-shaped gutters testify to the sophistication of Roman engineering.
Watermills were among the first technical facilities that did not rely on the muscle strength of humans or animals. It is known that in the Roman Empire they were used to make flour and sawing wood and stone. But the mills of Barbegal from the 2nd century AD were a specialty, as is evident from long-term research into the ruins. In contrast to the usually smaller individual mills of antiquity, it was a carefully planned large-scale plant that obviously enabled the mass processing of grain. It was estimated that the factory-like complex could produce tons of flour a day. An earlier study concluded that this mass production was probably used to make ship biscuits for the Mediterranean ports of the region in what is now southern France.
Limescale deposits allow conclusions to be drawn about wood structures
The functionality and technology of the system are still puzzling to archaeologists.
It is clear that the complex, built into a slope, had a total of 16 mill wheels and was supplied with water from above by an aqueduct. It flowed in two parallel rows of buildings on eight mill wheels each arranged one above the other. The upper parts of the facility were destroyed, however, and the wooden structures have crumbled, which is why the type of mill wheels and how they work has remained unclear. However, as the researchers working with Cees Passchier from Johannes Gutenberg University Mainz report, indirect references to the wooden structures have been preserved: Limescale deposits were discovered that had formed on the wooden components during use due to the water.
As part of their study, the researchers have now examined such a deposit, which allows conclusions to be drawn about a former wood structure. As they report, it is an imprint that apparently comes from an unusual, elbow-shaped gully that must have been part of the construction. “The shape of this water channel was not known from other watermills, neither from Roman nor more recent times,” says Passchier. “We were therefore puzzled as to why the channel was designed this way and what it was used for,” says the scientist. At first glance, a water channel shaped like this even appeared to be disadvantageous because it shortens the height from which the water falls onto the mill wheel.
A channel with a kink for optimal water supply
But the researchers’ analyzes and simulations then made it clear that the shape was apparently very useful. “We combined measurements of the water basins with hydraulic calculations and were able to show that the gully to which this elbow-shaped piece belonged very likely supplied the mill wheels in the lower basins of the complex with water,” says Passchier. “Our calculations show that the oddly shaped channel there was a unique adaptation for the Barbegal mills,” says the researcher.
The distribution of the calcium deposits in the elbow-shaped channel shows that it was inclined slightly backwards against the direction of the current. As the researchers explain, this ensured an optimal flow rate in the front, steep part of the channel. At the same time, the water jet was given a favorable angle and the right speed to optimally fill the blades of the mill wheel and thereby propel it. In the complicated mill system with the small water basins, this concept was more efficient than the use of a traditional, straight water channel, according to the scientists’ simulations. “That shows us the ingenuity of the Roman designers who built the complex,” says Passchier.
As the researchers further report, an additional finding emerged from the examination of the impression: They determined uniform vertical stripes, which are obviously impressions of the saw marks on the wood. “According to the characteristics, the wood of the gully was probably sawn with a mechanical, water-powered saw,” says Passchier. “The limescale deposits give us extremely exciting insights into the skills of Roman technicians at a time that can be seen as fundamental to our civilization,” says the scientist in conclusion.
Source: Johannes Gutenberg University Mainz, specialist article: Scientific Reports, doi: 10.1038 / s41598-020-74900-5