Under the Plaza de la Pescadería, and accessible through a modern glass structure, a cistern or 'castellum aquae' from Roman times has been preserved. Its construction has been dated to the 2nd century AD. and it is believed that it was in operation until the 5th century.

The cistern was built in 'opus testaceum' (fired brick) and was made up of three parallel naves, only one of which is accessible. It had total dimensions of about 45 meters long by 25 meters wide and it has been calculated that it had a capacity for 1,300,000 liters of water. It is believed that it was supplied through the aqueduct that reached the city from Alcalá de Guadaira, whose route would be reused in Islamic times for the construction of the Caños de Carmona.