Structure, evolutionary context and chronological data of the Monforte de Moyuela Roman dam (Ebro Basin, NE of Spain)

The Monforte de Moyuela dam, also known as Ermita de la Virgen del Pilar dam, is a Roman reservoir built on a tributary of the Aguasvivas River (Ebro basin, Spain). A multidisciplinary study has been carried out to investigate this kind of Roman water infrastructure. It is the fifth-highest dam (16.8 m) in the Iberian Peninsula and the seventh in the Roman Empire. The initial dam was built ca. 100 B.C.-10 A.D., probably in the period of Augustus, like other nearby Roman dams. It was quickly filled due to the extreme and generalized anthropic degradation in the basin during the Roman period. During the mid-2nd century, the wall was increased in height and its final silting was dated to the early 7th century. The study of the opus caementicium mortars shows constructive differences between the initial and subsequent phases of the wall. These mortars provided charcoal for dating the two phases. In addition, the stratigraphic and edaphological study of the reservoir's sedimentary fill, together with the C-14 ages, allowed us to reconstruct the two main activity cycles and the final siltation of the dam. Subsequently, the dam broke in two phases, which created the two stepped sections located on the current valley bottom. The data obtained allowed the creation of a geomorphological map and an evolutionary model of the valley showing the main differentiated stages, from the initial construction of the dam to its final opening. Although some remains of canals downstream of the dam have been identified, the use of this dam, which remained active for several centuries, still needs to be investigated in greater detail.