Roman dam of Cornalvo

The main dam wall is roughly 220 metres long and 18 metres high, with the inner face built as a stepped slope. It is made of large granite ashlars reinforced with lime mortar, rounded pebbles and rammed red clay. In front of the wall stands the Roman intake tower (the regulating tower), originally linked to the dam by a stone bridge, which allowed the flow towards the aqueduct to be controlled.

The associated conduit (the Cornalvo aqueduct, or Aqua Augusta) carried the water to the city through a channel (specus) 70 cm wide, lined with opus signinum, with a documented length of at least 70 km according to recent LiDAR survey.

The date of construction is disputed. The traditional proposal places it around AD 130, under Trajan or Hadrian; more recent evidence brings it forward to the 1st century AD, possibly the reign of Tiberius. And there is a more far-reaching idea: the archaeologist Santiago Feijóo (Consorcio de Mérida) proposes that the present dam wall may be Visigothic or Islamic, raised over the Roman aqueduct or after it had been abandoned.

It was declared a national monument in 1912 and is part of the Archaeological Ensemble of Mérida (World Heritage, UNESCO, 1993). It is still in use as a reservoir.