Aqueduct of las Ferreras (Tarraco), at Tarragone.
Acueducto de las Ferreras
Aqueduct of las Ferreras

Aqueduct of las Ferreras was built to take water to the city of Tarraco. From Gaya river, 92 m. high over the sea level, several canals were disposed: built at trenchs or inderground, depending on the ground. It ran from Francoli river valley 25 Km. up to the city. There, it was divided into two branches: one for the old area, another for the new one.
As can be supposed, most interesting sections of this construction were made when conduction should pass depresions, specially at the cross of ravine of las Ferreras. A series of archs for supporting water conduction measuring 215 m. long and 26 m. high were made. They were built with "opus quadrata": rectangular ashlars slighly padded placed without mortar.
This work shows outstanding technical features. It was composed by two orders of archs: upper with 25 archs, lower with 11. Distance between pillars axes was 8 m. with a gate between 5,90 and 6,40 m. Both series were crowned by cornices as wide as files of ashlars.
At lower series of archs, pillars supporting archs have stepped files of ashlars that made them become inverted pyramids, crowned by perimetral cornices -with a rectangular section- as wide as an ashlar. Archs are made with 19 or 21 voussoirs: that makes vaults of 1,85 m. There are common departing voussoirs to make a stronger structure for two consecutive archs. Sometimes second voussoirs join making tympanum scarce, with four or five files of ashlars.
Building of upper archs in line with lower is close to those of first order. Difference stays in pillars: they are not trunks of pyramids, but rectangular prisms.
On the last series of archs, conduction is made: the specus, between two walls of covered masonry. Sections with original pavement of opus signinum do remain.
Planta y alzado de la sección elevada del Acueducto de Las Ferreras
Plan and elevation of the upper section of the Aqueduct of Las Ferreras

It was constructed at Augustus Emperor age who made the city become the capital of Tarraconensis province. It is also known as Aqueduct of the Devil. It can be the first bridge-aqueduct with superimposed series of archs.