Writ in water—Unwritten histories obtained from carbonate deposits in ancient water systems

Calcium carbonate deposits from ancient water systems such as aqueducts are a hidden archive for archaeology and environmental sciences. These deposits formed wherever carbonate-rich water was in contact with a water-containing structure and recorded water composition, temperature, biological content, the operation or nonoperation of a water system segment, flow discharge and velocity, the shape of disappeared segments of water structures, the number of years a water supply system was active, disruptions of the water supply and water management such as repairs, adaptations and cleaning. Indirectly, urban development, resilience, population- and socioeconomic dynamics can be studied through the stratigraphy of carbonate in water systems. Carbonate archives can also give insight into long-term changes in paleoclimate and on environmental pollution, deforestation, extreme floods, droughts, earthquakes and volcanic eruptions. Archaeological and environmental investigations of carbonate deposits can provide data with up to daily resolution over decades to centuries. Although absolute dating of carbonate from water systems is still problematic, each study on the aqueduct of an ancient city, together with its carbonate deposits, provides its own microstory in Roman life.