Just oustside the city walls to the north is the Evora Aqueduct

Evora contains one of the Iberian Peninsula's greatest 16th century building projects, the Aqueduto da Água de Prata (the Evora aqueduct). The aqueduct provided clean drinking water to Evora by connecting the city to the nearest constant flowing river, 9km to the north. The channelled water flowed through a complex set of structures that included long tunnels, deep valleys and most impressively, over massive stone aqueducts. This clever design meant that the water from the river could flow unassisted into the Praça do Giraldo, the main plaza of Evora. Inside the city walls, the arches of the aqueduct reduce as they reach the terminus of the water flow. See: http://www.evora-portugal.com/Attractions/agua-de-Prata-Aqueduct-Evora-Aqueduct.html