A contemporary postcard view of an advanced stage in the construction of Careg-ddu dam in the Elan Valley. The normally submerged dam wall was to be of sufficient height to maintain the flow of water to Birmingham from a valve tower just upstream of this structure, the upper part of which carried a roadway giving access to the neighbouring Claerwen valley. The new building on the left was the replacement for the lost church of Nantgwyllt.