Canal de los presos del bajo guadalquivir:
The Lower Guadalquivir Canal (also known as the Canal de los Presos) is an irrigation canal, hydraulic infrastructure originally intended to irrigate an area of 56,000 hectares in the provinces of Seville and Cádiz. It currently irrigates an area of 80,000 hectares that falls under the Community of Irrigators of the Lower Guadalquivir.
It was built during the first Franco regime by several thousand political prisoners who were framed in the service of militarized penitentiary colonies, created in September 1939. They were the public works of the Franco regime that "for a long time [from 1940 to 1962] used political prisoners as the main labor force".