They solve the mystery of the flow of the Anio Novus, the longest of the Roman aqueducts

Mineral-rich waters from the Italian Apennines flowed through ancient Rome’s Anio Novus aqueduct, leaving behind a detailed rock record of past hydraulic conditions, the researchers say. Two studies characterizing layered limestone deposits—called travertines—within the Anio Novus are the first to document the appearance of antigravity growth undulations and establish that these features provide clues to the history of ancient conduction and storage systems. Water.

The Anio Novus was started by Caligula in 38 AD and finished by Claudius in 52 AD. It was the highest level of the aqueducts that entered the city of Rome, although in the time of Trajan the water began to become cloudy and he ordered the use of additional sources of the two upper lakes of the three created by Nero for his town of Subiaco, whose dams were the highest built in Roman times, as well as a filter tank close to the seventh mile of the Via Latina. The dams were destroyed by a flood of the Anio river in medieval times.

These multidisciplinary studies, led by University of Illinois Urbana-Champaign geology professor Bruce Fouke and published in the journals Scientific Reports Y GSA Special Papersapply advanced engineering principles and high-resolution microscopy to establish a controversial new theory about how the wavy travertine in the aqueduct formed, Fouke said.

Anio Novus Tour | photo Cassius Ahenobarbus on Wikimedia Commons

As the water flowed from the Anio River and an underground lake near Subiaco, Italy, it left behind wavy layers of calcium carbonate travertine that accumulated inside the floors, walls and ceilings of the Anio Novus aqueduct.

In the field, the researchers collected upstream and downstream oriented travertine samples that exhibit two prominent features: millimeter-scale patterns of light and dark layers, and centimeter-scale wavy shapes that persist in those layers.

Previous studies have proposed, without evidence, that the layers of the Anio Novus travertine are the result of flow changes initiated by seasonal changes or by engineering methods implemented by the Romans, the researchers said. However, travertine with similar bedding forms in ancient aqueduct systems occurs throughout the world, regardless of regional climate or exploitation.

Detail of the Anio Novus | photo Bruce Fouke

Fouke’s specialty is interpreting how microbes that thrive in mineral-rich water influence the crystalline architecture of travertine and other similar mineral deposits in nature. His group has worked intensively to reveal the geological history of stratified mineral formations, which makes it possible to infer life on Mars, through Yellowstone, to Australia’s coral reefs, and even inside the human body.

Subiaco’s waters are chemically similar to those in Yellowstone National Park, where aquatic microbes form mats and biofilms that play a key role in the shape and structure of Mammoth Hot Springs’ famous stepped travertines.Fouke explains. We have also identified fossil microbes and plant remains in the dark layers of the Anio Novus travertine deposits. Once we realized the similarity between the waters of Subiaco and Yellowstone, we knew we had the knowledge base and experience to begin unraveling the history and mystery of the last flow of the Anio Novus, the longest and most significant of the ancient roman aqueducts.

Fouke and Marcelo García, a U. of I. professor of civil and environmental engineering and co-author of the study, worked with their teams to meticulously measure the geometry of the undulating layers of Anio Novus travertines to make an unusual interpretation.

A sample of the ripple-marked travertine deposits of the Anio Novus Aqueduct in vertical cross section. The sample measures approximately 27 centimeters | photo Bruce Fouke

A geologist will tell you that the only way to form ripples is through fluid shearing and gravity-dependent sediment transport.Fouke said. The theory is that water or wind can move loose sediments in slowly advancing wave patterns that are influenced by gravity to form the familiar asymmetrical wave patterns we see along river banks, dunes, and in the ancient sedimentary rocks deposited in these environments.

However, Fouke’s team postulates that the Anio Novus travertine crystals precipitated, grew and accumulated in the running water of the aqueduct – independently of the forces of gravity and aided by the shape and biochemical composition of the microbial colonies. – to form what they call travertine crystal growth waves.

Although the complex processes that control travertine crystal growth ripples are clearly different from those that control sediment transport ripples, the researchers say they are visually similar. The geometries of the ripples along the vertical walls of the aqueduct are identical to those on the ground, demonstrating that the mechanisms that form the ripples of crystal growth do not depend on gravity.

Field photograph showing growth ripples of travertine crystals on the vertical side wall of the Anio Novus aqueduct on the Empiglione bridge | photo Bruce Fouke

Convinced that the structures are ripple marks that reflect flow, Garcia and his team measured the geometries of the ripples to reconstruct the volume and speed of water that flowed through the aqueduct during Roman times.

Because few researchers had previously recognized these structures as ripples, no one had used the power of a ripple shape, coupled with the principles of fluid mechanics, to produce this type of reconstruction.Garcia said.

Using travertine deposited in immediate contact with the original aqueduct mortar, the researchers conclude that when the aqueducts were first turned on, water flowed at a rate of approximately one meter per second, fast enough to flood a football field. in an hour, much faster than previously assumed.

The fact that there is wavy travertine along the roofs of the aqueduct channels indicates that they were operating at full capacity, according to the researchers. This observation suggests that earlier studies were incorrect in claiming that the layers formed due to seasonal change in flow or when the Romans used engineering means to control flow. These aqueducts were much more robust than previously believed.Fouke said. The flow was higher than anticipated, and that flow rate was constantly maintained.

Another detail of the Anio Novus aqueduct | photo Andrawaag on Wikimedia Commons

The researchers are now extracting the ancient fossilized microbes and their biomolecules trapped in the travertine to learn more about what kind of microbes – and possible pathogens – the Romans drank.

Historians and archaeologists are very interested in what led to the fall of the Roman Empire.Fouke said. Since the aqueducts played an important role in the success of the Romans, any information obtained from the disappearance of the aqueducts may be useful in this endeavor..


Sources

University of Illinois Urbana-Champaign | Duncan Keenan-Jones et al., Travertine crystal growth ripples record the hydraulic history of ancient Rome’s Anio Novus aqueduct, Scientific Reports (2022). DOI: 10.1038/s41598-022-05158-2 | Mayandi Sivaguru et al., Depositional and diagenetic history of travertine deposited within the Anio Novus aqueduct of ancient Rome, GSA Special Papers (2022). DOI: 10.1130/2022.2557(26)