Insights into the ancient Roman world: carbonate fragments unveil the secrets of Barbegal's Water Mills

The task of studying ancient structures based solely on their ruins presents a considerable challenge for archaeologists. This challenge was particularly apparent when examining the remnants of the Roman water mills in Barbegal, located in Southern France and dating back to the 2nd century CE.

The complex at Barbegal boasted a remarkable industrial setup, with 16 water wheels arranged in two parallel rows: eight wheels on the east side and eight on the west. These wheels utilized a cascading arrangement to harness the power of water. Initially, the ruins provided limited information, except for evidence of an aqueduct that brought the necessary water from nearby hills.

However, a significant breakthrough in unraveling this ancient complex's history came from the discovery of carbonate deposits. Professor Cees W. Passchier and Dr. Gül Sürmelihindi from Johannes Gutenberg University Mainz, in collaboration with colleagues from France and Austria, examined calcium carbonate deposits preserved in the Archaeological Museum of Arles.

These deposits had formed during the final phase of the mill complex's approximately 100-year operational lifespan. Initially, the researchers had to carefully piece together around 140 fragments of these carbonate deposits, akin to solving a jigsaw puzzle. Subsequently, the researchers employed various techniques, including mass spectrometry, to analyze the layers.

A key finding was that the wooden water wheels and channels required periodic replacement, typically between three to eight years. In some cases, old wheels were replaced with larger ones. The researchers deduced this by examining the unique shape of the carbonate deposits that formed in the water channels. Lower layers indicated lower original water levels, while upper layers suggested increased water levels.

Rejecting the notion of an initial insufficient water flow that was subsequently amplified, the researchers concluded that the inclination of the water channel must have been adjusted. The change involved altering the initially steeper slope with low water levels to a shallower slope suitable for higher water levels, which facilitated more efficient wheel operation.

Remarkably, isotope analysis of the carbonate layers provided further insights into the mill's lifespan. By analyzing variations in oxygen isotope ratios, the researchers could estimate the operating periods and identify the seasons when layers were deposited. They determined that the carbonate from the museum samples had accumulated over seven to eight years.

Additionally, the presence of mollusk shells and wood fragments exclusively in the topmost layer of carbonate indicated the mill's abandonment and subsequent disintegration. Though water continued to flow for a while, the maintenance of the water channels ceased.

The analysis of three distinct water channels revealed that the mills operated independently, at least towards the end of their lifespan. The layers in these channels demonstrated notable differences, with the western side of the complex being abandoned earlier than the eastern side.

Interestingly, after the mills were no longer in use, long carbonate pieces from the water channels found a new purpose as partition screens in a water basin for other industrial applications.

These findings provide valuable insights into the functioning of Barbegal's water mills. The ability to reconstruct the history of the mill complex using carbonate deposits demonstrates the significance of these fragments and highlights the meticulous research conducted by Professor Cees W. Passchier, Dr. Gül Sürmelihindi, and their collaborators. Through innovative analysis methodologies, ancient ruins can be transformed into windows into the past, shedding light on the fascinating world of the ancient Romans and their remarkable achievements.