Groundwater supply for Colonia Clunia Sulpicia (Hispania Citerior Tarraconensis)

Twenty centuries ago, a Roman authority founded a city on top of an inselberg where the discovery, by skill or chance, of a small aquifer which allowed access to a water supply for the city. In Roman times wells were drilled, of which nineteen reached a natural cavity. A horizontal gallery for water supply was also opened up, and a drainage conduct in the theatre was made to eliminate storm water. At some point, for natural or artificial reasons, the water table dropped and several wells dried up, forcing the descent of workers and other people to do additional work and to carve abundant graffiti and several clay figurines. The city did not survive the Middle Ages, the wells became cesspits and the ruins were plundered by neighbouring villages. It recovered its memory in the eighteenth century, in 1908 a Roman cave was rediscovered, the old water supply gallery, which gives access to the natural cave. This has been explored and surveyed by the Grupo Espeleologico Riberetio since 1980. From 2013, the Grupo de Technologias in Entornos Hostiles (University of Zaragoza) has carried out systematic radiolocation for the opening up of a direct access to the cavity. In addition, recognition of inscriptions with cavity scans and specific details have been made as well as the installation of two monitoring stations, both inside and outside the cavity to analyze the water performance of the system and the internal evolution of the CO2 content of the air in the cavity. The evolution of the piezometric level presents relatively important oscillations and a delay of two months is detected between the moments of heavy rains and the increase of water levels in the cavity. The CO2 content has a double periodicity, annual and daily.