El Atazar Dam is an arch dam built near Madrid, very close to where the Lozoya river joins the Jarama. It is the oldest dome dam in the world. The curved design of the dam is optimum for the narrow gorge in which it was built to retain water in the reservoir. Arch dams are thin and require less material to construct than other dam types. Construction started on the dam in 1968 and finished in 1972. The dam is 440 feet (134 m) high and 171.6 feet (52.3 m) wide at the foundation. The reservoir capacity is 344,000 acre feet (424,000,000 m3). It is a double curvature concrete arch buttress design.