Segovia (Spain)

Roman aqueducts: Segovia (Spain) Segovia - SEGOVIA
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Segovia was a small Roman town on a steep isolated hill at the junction of two rivers on the main road from Emerita (Merida) to Caesaraugusta (Zaragossa). Despite its small size, the town was supplied with water by an impressive aqueduct which was built sometime in the first or second century.


Segovia and its surroundings

Segovia is well known for the magnificent aqueduct bridge in the centre of town, one of the largest and best preserved in the Roman empire. The Roman aqueduct channel of Segovia has a total length of 15 km from its source in the mountains to the Alcazar on the NW tip of the city, and the aqueduct bridge is only a small part of this structure. Segovia is special not only because of the artistic marvel of the aqueduct bridge and medieval buildings, but also because of its setting in the wide open fields of Castille at the foot of the mountains, and the possibilities this gives to appreciate the layout of its aqueduct.

The aqueduct obtained its water not from springs, but from a small river in the Sierra de Guadarrama. Although the Romans favoured springs for aqueduct water because the risk of contamination is less, this is not everywhere possible because of the local geology. Large springs are most common in limestone areas, and the mountains surrounding Segovia are mostly gneiss and granite. In this case, a small ledge of stone set was set oblique to the course of the stream and this directed water into the aqueduct channel. From this source at 1255m altitude, the aqueduct channel followed the contour lines along the west side of a spur of the mountains known as the Cabeza Grande with a slope of 0,43%. The channel was mostly a buried structure with internal dimensions of 0,6 x 0,6 m. At the north side of the spur, the channel suddenly descended steeply by 75m over only 553 m, a slope of 13,5%, to the crossing of the next major creek, the Fuentecilla de Tilviejo. From here, the aqueduct ran along the top of a long spur of hills straight towards the city as a channel covered with granite slabs. About 1 km before the city walls, the aqueduct had to cross a 30m deep valley. This was done by a short section of a wall and a series of arches of one and two tiers, the famous "aqueduct of Segovia". After reaching the town wall, the conduit was buried again but it seems that the aqueduct channel continued up to the Alcazar, including a cleaning basin in the Plaza Mayor. Since the Alcazar is at the lowest part of the city, a distribution basin or Castellum Aqueae must have been present close to the end of the aqueduct bridge, at the highest part of the city.

Segovia from the air
The original construction of the aqueduct seems to follow common engineering practice of early Imperial Age. A curious phenomenon is the steep section of the channel at the north side of the Cabeza Grande mountain spur. This could be due to a two phase construction of the aqueduct; possibly, a first aqueduct of only 9 km length was constructed to the headwaters of the Fuentecilla de Tilviejo creek. When this did not produce enough water year round, a second section was built towards the Aceveda river. It is also possible that difficulties in the terrain made it necessary to choose this complex trajectory.
Along the course of the aqueduct, several cleaning basins have been found, and many more probably existed. These basins are known in Spanish as a "desarenador" (de-sander). Structures of this type were common along Roman aqueduct channels, especially in aqueducts like that of Segovia which carried "soft" water from a granite source that did not deposit sinter in the channel. As a result, sand was not only transported from the river source upstream, but the channel eroded constantly by dissolution of cement that was used to bind the stones of the conduit. Several basins were therefore needed to catch this sediment, and frequent repair jobs were needed on the actual channel to keep it reasonably waterproof.

The aqueduct of Segovia is special in that it has been used almost without interruption from Roman times to the present day. As a result, many parts of the aqueduct are still with us, and the bridge certainly survived because of its usefulness for the local water supply; it could easily have been recycled into churches and monasteries, like in so many other Roman towns. The longevity of the aqueduct also means, however, that little of the original Roman aqueduct channel survived, because parts of it have been used and reused over the centuries by Romans, Visigoths, Arabs, and Castillians. The most drastic measure was taken in 1929 when concrete pipes were put in place to replace the Roman channel completely. Most other remains of the old channel must have been removed at that time.
The aqueduct bridge in town and the cleaning basins underwent restoration many times, most recently in the 1970s and 1990s. A book (Gallardo 1975) and web sites testify to this restoration work and ongoing efforts to preserve the structure. All car traffic has now been banned from near the bridge to reduce the danger of vibration and pollution. The aqueduct of Segovia is in excellent shape and maintenance, and will hopefully be a landmark for many years to come.

Visible remains


Source of the aqueduct

Location: 40.85173N, 4,06881W (WGS84)
The caption of the aqueduct of Segovia lies in a small mountains stream, the Rio Aceveda, headwaters to the Rio Frio, in pine and oak forests on the northern slopes of the Sierra de Guaderrama at 1255m altitude. The caption is one of the best preserved Roman structures of this type in existence. It consists of a narrow ledge or weir of gneiss blocks at a spot there the valley is slightly wider and not hammed in by steep gneiss outcrops. The weir is 11 m long and consists of 26 gneiss blocks, 69cm long and of variable width, held together with (modern) iron clamps in lead, which mimic the original Roman setting and use the small holes in the stones.
The source
The weir lies at approximately 45 ° to the axis of the river and channels the water to the north side of the stream, where it is led into the actual aqueduct channel with a maximum debit of 50 litres per second. The head of the aqueduct is made of large nicely worked granite blocks. A modern steel sluice gate can close off the channel, but a ledge in the stone suggests that the Roman caption used a sluice gate as well, possibly of wood.
This kind of weir is known in Spanish as an "azud", and the channel leading away from such a dam a "caz". Like most words to do with water in Spanish, these are derived from Arabic.

Valdeconejos bridge

Not far from the source, the aqueduct channel had to cross the small brook of Valdeconejos (valley of rabbits). Here is an interesting structure in the form of a small bridge of 5 granite plates that still serve their original purpose of leading the water of the small creek of Valdeconejos over the top of the aqueduct channel. In most Roman aqueducts, the channel is lead on a bridge over small drainages, but here the opposite solution was chosen.

How to reach these sections

Both the Azud (the source) and the Valdeconejos bridge can be reached on foot in about 1 hour (3km) from the village of Revenga. Park in Revenga or at the entrance of the road that runs along the north side of the Embalse the Puenta Alta Lake. Follow the road to the parking beyond the end of the lake and then follow the yellow aqueduct signs up the hill. From the parking, take the track that goes up steeply and passes through the fence, follow this to above the creek on the north side until the track reaches some meadows; cross the creek here, and follow the yellow signs steeply up the hill till reaching the aqueduct channel at 40,85727N, 4,07430W; this can be recognised by the box-shaped maintenance shafts that have been installed on the water pipe in the early 20th century. Follow the track now along the contour lines towards the captions upstream (to the right, sign to "azud"). On the way back, the aqueduct can be followed past Valdeconejos until reaching the track that descends again to Revenga. It is even possible to follow the aqueduct all the way to the city. The tourist information in Segovia can organise trips to the aqueduct source, and has a brochure (in Spanish) describing three walks along the course of the conduit, from the mountains to the city.

Remains of the channel

Along the track that follows the hilltop between Segovia and the mountains, several fragments of the Roman channel can be seen. This includes parts of the actual channel, and some granite cover stones.

To see these remains, either take the small asphalt road that leads east from the Revenga-Segovia road up to a farm on the north side of the road, and walk from here north or south. Alternative is to walk south from the city or from the Segovia - San Ildefonso road towards the track of the channel. The new high speed train between Segovia and Madrid unfortunately cuts the track of the aqueduct, but it can be avoided on the east side. The approximate trace of the aqueduct can be seen on air photos because it is followed by an artificial open channel that provides water to the surrounding vegetation. At some time during the history of the aqueduct, it apparently functioned as a open channel. Nearby can be seen remains of several stages of the aqueducts operation in a 100m wide zone, including the pipeline from the 1920s.

Casa de Piedra or "el Caserón"

Along the west side of Avenida Juan de Bourbon y Batenberg, before reaching the Plaza de Toros, lays the first cleaning basin of the aqueduct. This basin is in a small concrete building, known locally as the Casa de Piedra or el Caserón. It has is 5,50 x 5,90 m with a door on the north side and a window in the opposite wall. The aqueduct entered from the south and left at the north side and passed through a basin of 2,25 x 3,10 m and 2m deep. The basin could be cleaned by means of a side channel to the west of the same depth as the basin, which could be opened with a sluice to flush out the basin. The channel that leaves the building on the north side is not the original Roman aqueduct channel but a later replacement with a diameter of 0,30 x 0,30 m. The building itself is at least partly Roman.

Aqueduct wall

At the junction of the Calle del Coronel Rexach and the Avenida del Padre Claret is a small monument that marks the start of the most spectacular section of the Segovia aqueduct. The cylindrical stone is a monument from the 17th century, found close to Segovia. It has been placed on the wall that originally supported the Roman aqueduct channel, and which now carries its narrower successor, a 30 x 30cm channel from the 15th century. This wall, 141 m long and 1,4 m wide, runs up to a building that covers the second and final cleaning basin before the aqueduct bridge.
Casa Aqua

Casa de Aqua

This building, 8,90 x 7,50 m is known locally as the Casa de Aqua. Inside is a basin of 4,25 x 2,18 m, 2,90 m deep with an entry and exit of the aqueduct channel. Contrary to the Casa de Piedra, there is no channel at the base of the basin, so that any sediment that accumulated had to be removed by hand, and could not be flushed out. There is a diversion channel on the west side of the building, but it probably only served to skim off floating debris like leaves and branches before the water entered the aqueduct bridge where any dirt would be extremely difficult to remove. The building is at least partly Roman.

Aqueduct bridge

The aqueduct bridge of Segovia starts at the Casa del Aqua. A 42 m long section of wall is followed by a 683 m long bridge of arches in a section that changes direction several times. The corners where the bridge changes direction have not been strengthened in any way. A first section of 75 singe arches is followed by the most famous section of two tiers and 44 double arches that crosses the valley close to the city wall with a maximum elevation of 29 metres. The aqueduct bridge is completely built in opus quadratum, large blocks of granite without the use of cement. This method of construction is probably imposed by the lack of limestone to make cement in this part of castille, but helped to preserve the building by making the bridge flexible to survive small earthquakes, settling and small motions due to wind and temperature gradients. The ornamentation of the bridge is sparse and restricted to imposts along the tops of the spandrels, at the springing of the arches, and in the piers. The imposts were probably meant as ornamentation, but also to carry the formwork to build and maintain the bridge. The diameter of the piers decreases stepwise by one Roman foot upwards at the imports from 3 x 2,4 m at the base of some pillars to 2,5 x 1,8 m at the top. Because of the decreasing diameter of the piers, the arches increase in span from 4,5 m to 5,1 m at the top.
The aqueduct bridge
The aqueduct is special in that nearly every pillar and spandrel has a different design. Some arches have a common springer, others have spearte but touching ones, and the base of many of the spandrels is different. This may partly be due to later reconstruction, but especially in the two tier section of the bridge, the design seems to be original. This would imply that the bridge was not designed in advance in great detail, but that arches and spandrels were designed on the spot with the bocks that happened to be available and designed as construction progressed.

Segovia is mostly underlain by soft sandstone, but the hill to the east where the bridge starts consists of gneiss. The aqueduct pillars are either set directly on the gneiss, or in foundation pits that have been excavated in the soft sandstone, mainly in the double arched part of the bridge. The Roman engineers apparently realised the different properties of the two rock types, and decided to take no risk with the sandstone. A gneiss outcrop supporting a pillar can be seen in one of the last pillars of the single arch section, before the final bend that leads to the city (pillar 71)

The bridge is built from approximately 20.400 blocks of granite, 7.500 m3 of granite with a total weight of 20.000 tons. The largest block in the bridge has a weight of 2 tons, and blocks of 1.000 kg are common. The granite was obtained locally from granite outcrops NE of the city up to 5 km away. Since no quarries have been found that can have produced such a large amount of granite, it is assumed that the blocks were obtained from large granite boulders that dotted the landscape at that time; presently, there is a marked absence of large granite boulders close to Segovia.
Small holes in most of the granite blocks of the bridge indicate that the bridge was built using cranes with grips that tightens when weight is suspended.
The rounded, bossed form of the granite blocks of the aqueduct is partly original, but also enhanced by weathering of the relatively soft granite in the course of time.

The deck of the bridge carries the specus of the aqueduct, but this is actually a pile of concrete which has gradually been added to over the course of the life of the bridge; the Roman section is probably buried somewhere in the lower part. Most of the specus and the channel presently visible at the top of the aqueduct date from the 15th century. This channel, 30 cm wide, is much smaller than the Roman specus which was 0,6 x 0,6 m. The present slope of the channel along the top is variable, but is mostly below 1%.

The small section of wall of 16 x 2m in the second tier of the aqueduct over the centre of the bridge was initially meant to carry an inscription and statues, possibly of Hercules, the legendary founder of Segovia. The bronze letters have long since been removed, and the only thing left are the holes that were used to attach the letters to the wall. Several suggestions have been made for a reconstruction of the inscription, based on the shape and setting of these holes, but no agreement exists to date. The aqueduct has therefore been attributed to Claudius, Trajan or Nerva, depending on the reconstruction. The two most quoted reconstructions are:

IMP NERVAE TRAIANVS CAES AVG GERM P M TR P II CO S II PATRIS PATRIAE IVSSV
P. MVMMIVS MVMMIANVS ET P. FABIVS TAVRVS IIVIRI MVNIC FL SEGOVIESIVM
AQVAM RESTITVERVNT

Or an older one:
TI ClAVDIVS PONT MAX VIII COS III TRIBVNICIA POTESTATE VIIII IMP PP OMNIVM FECIT

Parts of the aqueduct bridge have been torn down or collapsed during its long history, especially in the lower, upstream part. Every time this happened, it has been fatefully reconstructed, although not always with the original stone and design. As a result, several of the first upstream arches have a distinctly un-Roman pointed profile to them.

The section in the city

At the top of the bridge, just inside the city wall, are four arches preserved of an original arrangement of 9: these arches carried the aqueduct up to a section of wall with a sharp curve to the west, towards the centre of the city and the Alcazar. No Castellum Aquae has been found to day, but this may have been present somewhere in the first section after the bridge. Recently, a cleaning basin and section of the aqueduct was found below the Plaza Mayor.


Cees Passchier

Segovia - SEGOVIA

Item Info
Length 14,965 km
Cross-section 0,6 m x 0,6 m
Volume 1800 - 4500 m3/day
Gradient 1,6 %
Period Augustan
Features
  • river intake
  • aqueduct bridge


Recommended literature :
  • Supervivencia de una obra hidráulica: el acueducto de Segovia, by Aurelio Ramírez Gallardo (1975)
  • Tras la huella del aqueducto., by Charo Domínguez and Cristina Pampillón (2007). Ayuntamiento de Segovia
Recommended website   :
How to visit                  : see above
HOME More literature on more aqueducts Last modified: November, 2007 - (webmaster)


Sketch map
Weir in Aceveda River
Weir at the source
Detail of the weir

Sluice gate
Bridge of Valdeconejos
Coverstones
View from the north

View from the west
Interior of the Casa
Southern side of the Casa
Channel below the doorway

Bulb as a filter
Inside the Casa de Aqua
Looking downstream
Single arches

Reused stone
Overflow
Base of a bridge pier
Start two-tier section

Detail of a pier
Central part
Evening view
Aerial view

Bridge with niche
Bronze letters have been removed
The 15th century channel
pier 117

Final section of arches
Early morning view
GoogleEarth View of Segovia
Typical hoisting grip