Alconétar Bridge

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Puente de Alconétar
Remains of the Alconétar bridge with its flat arches
Crosses Tagus
Locale Garrovillas de Alconétar, Cáceres, Extremadura, Spain
Design Segmental arch bridge with voussoir vaulting
Material Stone
Total length 290 m
Width 6.55 – 6.80 m
Height Minimum 12.50 m
Number of spans 16 (without flood outlets)


Arch of western abutment

The Alconétar bridge was a Roman bridge on the river Tagus in the province of Caceres in Spain. Also known as Puente de Mantible, it is one of the oldest stone segmental arch bridges in the world, predating other examples such as the Zhaozhou Bridge in China and Ponte Vecchio in Italy (both of which are still in use today). In 1970 the bridge was relocated from its original position when the Alcántara reservoir was created in the province of Cáceres, Extremadura, Spain[1].


This needs to go into the INFOBOX (somewhere) ... span 7,20-15m pillar thickness ca 4,4 m arc size (crown) 1,20m (2nd flood outlet) span-to-rise ratio 4-5:1 discharge profile 73% arch slenderness 6:1 (2. flood outlet), date of origin probably between 98 and 138 A.D., Condition ruin The remains of the bridge were moved upstream to a new location in 1970.)


[edit] Location and access by road

The historic Alconétar bridge, which should not be confused with the monumental Alcántara Bridge further downstream, was part of the important Roman road Via de la Plata and crossed the River Tagus not far from the mouth of the river Almonte in the heart of the Spanish province Cáceres in the region of Extremadura.[2] A modern motorway and a railway, which cross the River Tagus nearby, provide convenient access to the Roman bridge. During the building of the Alcontéra dam in 1970 the remains, mainly to be found on the right side of the river, were relocated. The ruins that are visible today were moved to a meadow six kilometers to the north of its original position and close to the municipality of Garrovillas de Alconétar.[3] There are no real remains of the neighbouring ancient bridge on the river Almonte.[4]

In the classical period, the Alconétar bridge was part of the Roman road Iter ab Emerita Caesaraugustam, that was later called Via de la Plata. This important inner Iberian connection led from the provincial capital Mérida in the south, through the river valleys of Alagon, Tiétar and Tagus to the north, then on to the eastern part of Meseta Central, passing the major towns of Salamanca and Léon.[5] Apart from the junction over the Tagus the remains of four other ancient bridges can be found along the road: one over the Albarregas, another over the Aljucen, a third close to Caparra and a fourth over the Tormes.[6] In the hills overlooking the Alconétar bridge a Roman Mansio with the name of Turmulus (Span. Turmulos) was established, according to the customs of the time. It was the fourth of a total number of 16 between Mérida und Astorga.[7]

[edit] History

The exact date when the Puente de Alconétar was built is unknown because of missing literary and epigraphic sources.[8] The ancient construction with its elongated arches, however, is one of the earliest of its kind. Its extraordinary segmental arches suggest that it was built in the early second century AD, more specifically in either the era of Emperor Trajan (98-117 AD) or Hadrian (76-138 AD), as this type of construction is typical of that era. Trajan was born in the Spanish province of Baetica and ordered the Iter ab Emerita Caesaraugustam's restoration when he came to power.[9] Segmental arches were often used by Apollodorus of Damascus, Trajan's court architect, as for example in Trajan's Forum and most notably in the greatest civil engineering structure of its time: Trajan's Bridge was made of wooden arches set on twenty masonry pillars (made with bricks, mortar and pozzolana cement) in the early 2nd century. It stretched for over 1000 metres over the Danube and was used during the Dacian Wars for deploying troops.[10]

Moorish geographers make no mention of this ancient bridge, even though they praise the Roman bridge of Alcántara which leads across the Tagus as well.[11] There is some evidence that a community called Alconétar, Alconétara or Alcontra (Arabic: small bridge) existed at least temporarily - probably an indirect reference to the high-reaching bridge of Alcántara.[4] It also remains unknown, why the bridge of Alconetar is called Puente de Mantible in the local vernacular; this is an expression alluding to a legend of Charlemagne and his Twelve Paladins.[12]

The bridge was probably in use until the time of the Reconquista, when the Tagus constituted the border between the Christian and the Moorish range of power from the eleventh to the thirteenth century, but the frequent clashes might have easily made the bridge unusable.[13] According to another theory the water could have begun to wash away the ancient foundations.[13]

The Puente de Alconetar is first mentioned in records in 1231 and in 1257; this second mention states explicitly that the bridge was in use at the time. It was probably repaired by the Knights Templars who, in the meantime, had decided to look after the bridge as well as the village. Arches 1 and 3, which were replaced, are said to date back to this era. Around 1340 the bridge was, however, apparently unusable again, so boats were used to cross the river; their use is also recorded at later dates. On the site of an ancient resting place, a fortress was erected in the Middle Ages. Its tower, made of Roman spolia, overlooks the valley to this day.

There have been several attempts to reopen the bridge in the modern era but none were successful. In 1553, the architect Rodrigo Gil de Hontañón proposed 80,000 Ducats for the reconstruction of the bridge without ever realising his plans. The construction project of Alonso de Covarrubias and Hernán Ruiz of 1560 never went beyond the planning stage, and neither did another project between 1569 and 1580.

In the 18th century two attempts to repair the bridge failed, in 1730 and 1760/70. The latter plan of the military engineer, José García Galiano, included a complete reconstruction with three wide-spread flat arches. The planning sketch shows that already at that time the remaining arches appeared on the right bank only, which the drawing of Fernando Rodríguez from 1797 and the excellent engravings in Alexandre de Labordes' Voyage pittoresque de l'Espagne a few years later confirmed.[5] The reconstruction sketch produced by Rodriguez (see image below) shows the profile of the bridge, rising evenly and dominated by three central arches in the centre of the river. These arches are flanked by a further nine segmental arches on both sides. The symmetry of the arches suggests that, instead of the fortification upstream on the right bank, there might have been another segmental arch in Roman times.[14]

Antonio Prieto, a civil engineer, laid the basis for modern scientific analysis of the bridge in 1925 with his survey, which details the condition of the bridge before its relocation. Although this was a serious attempt to recontruct the bridge as close to the original as possible, slight changes to the main body can never be, according to Duran, excluded in the course of such an attempt.[15]

[edit] Construction

Outline of the remaining structures
Arch number 3. The right pillar, no. 3, is the best preserved; the sloping support for the Roman segmental arch is easily recognisable.
Sideview of pillar no. 3: The positioning of the pillars in relation to the ancient segmental arches can be calculated using the degree of curvature of the originally preserved supports for the arch.

(Where? Two original segmental arches were preserved, of 6.7 m (22 ft) and 7.2 m (24 ft) span, and a span-to-rise ratio of between 4 and 5, as were segmental arches from a later date.[16] There is evidence from the position of piers that segmental spans up to 10 m (33 ft) may have been present in the original construction.)

The main features of the Alconétar Bridge are the segmental arches which were used rather infrequently in ancient bridge building. According to Prieto the bridge had sixteen arches, not including the high water passage on the right access, with the following spans (estimates are in brackets, units are in meters):

7.30 – 8.20 – 9 – 10.15 – (11 – 12 – 13 – 14 – 15 – 14) – 13 – 12 – 11 – (10) – 9.30 – 9.10. [8]

Other sources however estimate between eleven and fifteen arches.[17] The total length of the linear structure was 290 metres, of which 190 metres spanned the riverbed at low water.[4] If one adds the span of the arches and assumes, on the basis of the preserved pillars, an average pillar strength of 4.4 metres, then the distance between both bridge ramps would have been 244 metres (= 178 15 x 4.4), which corresponded to a river cross section of 73%.[3] In comparison; the corresponding figures of the Roman bridges of Córdoba, Mérida and Salamanca were 62%, 64% and 80% respectively.[18]

Before the repositioning, the preserved structural fabric was mostly found on the right bank of the Tagus where the current was less strong; a number of pillar butts rose just above the water surface in the middle of the river, whilst on the left bank a further two pillars remained standing, to which the left abutment was connected. [19] The remains, that were secured before the flooding of the Alcantara reservoir in 1970 (see photographs), were essentially: the right bridge ramp with the two arch-shaped flood openings, the pillars 1, 2, and 3 with the supports 4 and 6, as well as the arches 1 and 3.[3]

The approach to the ramp is 42 meters long and 6.55 to 6.80 meters wide. The clearances of the two segmental arches in the skew arch are 6.95 and 7.40 meters long, which corresponds to a camber of 4.0 or (rather) 3.3 to 1. The accurately fitting inclined contact surface for the abutments clearly proves the Roman origin of these arches. With an extraordinary width of 1.20 meters, the keystones appear oversized in relation to the span (a ratio of 1:5.8 or 6.2). In contrast, both the conserved bridge arches, numbers 1 and 3, are instable substitutions, made of carelessly walled rubble. The age of these arches is unknown, as with all other repairs. Possibly they were built around the period of the Knights Templar.

A likewise obviously post-classical construction is the brickwork of the first two pillars above the lower molding, which projects from every pillar at the same height. The superstructure of the pillars could have been reconstructed for a drawbridge or a tower, which, according to an illustration in the Voyage Pittoresque, rested upon pillar 2. In contrast, the Roman building material is preserved up to the top at 12.50 meters. The thoroughly worked ashlar and the second molding, characteristic of all classical pillars, provide us with the most distinct impression of the original shape of the Roman bridge.

It is possible to relatively exactly reconstruct the pitch (rising height) of the original segmental arches on the basis of the angles of the inclined contact surface for the spring of the arch. Thus, the third arch originally (primarily) drew a sector of 95°, which allows the suggestion of a rise-span ratio of about 4-5 to 1 for the other segmental arches. De Labordes´ engravings approve this value (number). According to them, an intact Roman segmental arch spanned over the adjoining fourth bay. Along with other earlier examples, such as Limyra Bridge or the Ponte de San Lorenzo, the Bridge of Alconétar therefore ranks among the oldest segmental arch bridges in the world. In contrast to what had previously been widely believed and taugh, this is evidence that Roman brigde builders possessed detailed knowledge of flat arches.

The widths of the pillars increase slightly towards the middle of the river, 4.25, 4.45 and 4.55 metres, while the intervals increase from 7,30 to 10.20 metres. The fifth and last pillar carries the distinctive nickname “Bishop´s table”. It possesses by far the largest cross-section and stands alone in the middle of the river. It might be a medieval pillar which could have been installed instead of two antique arches as a base for a watchtower. All five pillars are strengthened on the upstream side by pointed cutwaters.

The wall of the Aconétar Bridge consists of blocks of granite. The inner parts of the pillars were filled with Roman concrete, which was a common method applied for Roman bridges. Outwardly, the extraordinary flat segmented arches, uncommon during the classical era and afterwards, must have given the bridge a rather compact appearance and would have made the road over the bridge either flat or slightly convex.

[edit] Reconstruction and Measurements

Reconstruction attempt by Fernando Rodríguez in 1797 (view upstream). The then existing remains are coloured in stronger shades.


[edit] References

  1. ^ Troyano, Leonardo Fernández, "Bridge Engineering - A Global Perspective", Thomas Telford Publishing, 2003
  2. ^ Prieto 147
  3. ^ a b c O'Connor 108f.
  4. ^ a b c Prieto 149
  5. ^ a b Durán 182
  6. ^ Durán 92f.
  7. ^ Gil 9f.
  8. ^ a b Prieto 155
  9. ^ Prieto 155; O'Connor 108f.
  10. ^ O'Connor 142f.
  11. ^ Prieto 10f.
  12. ^ Prieto 158
  13. ^ a b Prieto 155f.; Durán 182
  14. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Dur.C3.A1n_183; see Help:Cite error.
  15. ^ Durán 181, 184
  16. ^ "A brief analysis of the Roman bridges of the way La Via de la Plata", Limón, Hortelano & Fernández
  17. ^ Durán 184
  18. ^ O'Connor 165
  19. ^ Prieto 150f.

[edit] Further reading

  • Casado, Carlos Fernández: "Historia del puente en Espania. Puentes Romanos: Puente de Alconétar", Instituto Eduardo Torroja de la Construcción y del Cemento, Madrid 1970 without page numbers
  • Fuentes, Manuel Durán: "La construcción de puentes romanos en Hispania", Xunta de Galicia, Santiago de Compostela 2004, ISBN 9788445339374, pp. 181–87
  • Gil Montes, Juan: Via Delapidata. In: Elementos de la Ingeniería Romana, Congreso Europeo: Las Obras Públicas Romanas, Tarragona 2004.
  • Limón, Teresa González et al.: "A Brief Analysis of the Roman Bridges of the Way 'La via de la Plata'", Lourenço, P. B./Roca, P. (ed.): Historical Constructions, Guimarães 2001, pp. 247–256
  • O’Connor, Colin: "Roman Bridges", Cambridge University Press 1993, ISBN 0-521-39326-4, pp. 108f., 171
  • Vives, Antonio Prieto : "El puente romano de Alconétar", Archivo Español de Arte y Arqueología, Vol. 2 (May/Aug. 1925), pp. 147–158

[edit] See also

[edit] External links

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Full list of Roman bridges

Coordinates: 39°45′14″N 6°26′14″W / 39.753838°N 6.437345°W / 39.753838; -6.437345

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