Barragem do Muro
Nossa Senhora da Expectação, Portugal
The Muro Dam was a Roman dam in Portugal. Located near the eastern municipality of Campo Maior, it is the largest surviving ancient dam in the country south of the Tagus river. The 174 m long structure features three slight bends in its course. Its downstream side is supported by a series of thirteen small buttresses at intervals of 3–4 m. The central section, where the dam is highest and strongest, is further strengthened on its air-side by three vertical arches which go from buttress to buttress.
Archaeological site data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).