Alcantarilla Dam

The Alcantarilla Dam is a ruined Roman gravity dam near Mazarambroz in Toledo province, Spain, believed to date to the 2nd century BC, making it possibly the oldest known Roman dam. Standing 20 m high and at least 550 m long, it was built using opus caementitium and opus incertum masonry to supply water to the city of Toletum (Toledo) via an aqueduct passing through Layos. The dam and reservoir were constructed on a tributary of the River Tagus, but the structure may have been breached in antiquity due to insufficient strength.