The Romans built dams in Spain on a scale that still surprises engineers, and Proserpina, a few kilometres north of Mérida, is one of the best preserved. It was built in the first or second century AD to store water for Emerita Augusta, the provincial capital, which was fed by aqueduct from the lake. The dam is a massive earthen embankment faced with stone and backed by huge buttresses, some four hundred metres long, and it has held water for roughly nineteen centuries with repairs. The reservoir, a long green lake in a landscape of holm oak and rock, is now a place where local people fish, swim and walk.
The name of the dam comes from the goddess Proserpina, whom Roman citizens honoured with a small temple that stood near the shore. Mérida itself, six kilometres away, was founded in 25 BC for veterans of the army and became one of the great cities of the empire in the west, and you can still visit its theatre, amphitheatre, circus, bridge over the Guadiana, and the arches of the Los Milagros aqueduct, which carried water from Proserpina to the city. UNESCO listed the whole as an archaeological ensemble in 1993.
The approach is easy riding. Quiet lanes lead from Mérida through farmland to the reservoir, with gentle bends and dehesa on either side, and the surfaces are generally good. On summer weekends locals come to the water and cars park along the verge, so watch for pedestrians and children. The heat is a serious matter from June to September, and the best times are spring and autumn. Storks and kites circle overhead, and the air smells of dry grass and thyme.
Mérida has everything you need: fuel, supermarkets, restaurants and rooms, and nearby Esparragalejo and Mirandilla have smaller services. Look for cured ham, a rich stew of pork and chickpeas, or torta del Casar, a soft sheep's cheese from the region that you eat with a spoon. Take water, and a hat, and allow an hour to walk along the dam and across the top, where you can see the water on one side and farmland on the other, the same view the Romans engineered.