Carbonate Deposits Shed Light on Byzantine Water Management

The advancement of scientific tools enables us to peer back into the history, uncovering engineering techniques used by those who lived many years ago: A team of researchers from Johannes Gutenberg University Mainz (JGU) has revealed new information about the upkeep of the world's longest aqueduct of the time, the 265-mile-long (426km) Aqueduct of Valens supplying Constantinople, now Istanbul in present-day Turkey.

The study, published in the journal Geoarchaeology, focuses on this spectacular late-Roman aqueduct, revealing the channels had been drained of carbonate deposits just a few decades before the site was abandoned, according to a press release.

The longest aqueduct of the ancient world

To give you a bit of historic background, Constantinople was named the new capital of the Roman Empire back in AD 324, by the Roman Emperor Constantine the Great. A new aqueduct had to be built to provide Constantinople with freshwater from springs 37 miles (60km) to the west, and as the city developed, the system was expanded to springs 75 miles (120km) away in the fifth century.

This made the aqueduct the longest of the ancient world, giving it a grand length of at least 426 kilometers. Broad vaulted masonry channels, 90 large, stone and concrete bridges, and tunnels up to 3 miles (5km) were all part of the design.

The researchers led by Dr. Gül Sürmelihindi from the Geoarchaeology group at Mainz University studied the carbonate deposits from the aqueduct to learn more about its history. Carbonate deposits can tell a lot about water management and the palaeoenvironment at that time: They are the limescale that form in the running water and can block the entire water supply in some cases and have to be removed from time to time.

The entire aqueduct system was discovered to have only thin carbonate deposits, indicating some 27 years of operation. This didn't make sense, however, since the aqueduct system was believed to have been operational for over 700 years.

"This means the entire aqueduct must have been maintained and cleaned of deposits during the Byzantine Empire, even shortly before it ceased working," explained Sürmelihindi.

Although the aqueduct is late Roman in origin, the carbonate found in the channel is from the Byzantine Middle Ages. This made the researchers think about possible cleaning and maintenance strategies—because cleaning and repairing a channel of 426 kilometers implies that it cannot be used for weeks or months, while the city population depends on its water supply.

The carbonate dates from the Byzantine Middle Ages, despite the fact that the aqueduct is late Roman in origin. This prompted the researchers to consider alternative cleaning and maintenance solutions since cleaning such a long channel which a lot of people depended on would take weeks to months.

This led researchers to the discovery of the 31 miles (50km) of the central portion being constructed as a double canal, with one aqueduct channel crossing the other on two-story bridges. "It is very likely that this system was set up to allow for cleaning and maintenance operations," said JGU Professor Cees Passchier. "It would have been a costly but practical solution."

One of its biggest bridges, Ballıgerme, was blown up with dynamite in 2020 by treasure hunters who thought they could find gold in the ruins, so it's not possible for the researchers to figure out how the whole thing operated. However, this aqueduct still remains a remarkable example of Roman engineering and architecture, and perhaps, it could still provide insights into the technological facets of construction and usage.