Alconétar Bridge
Encyclopedia
The Alconétar Bridge also known as Puente de Mantible, was a Roman segmental arch bridge in the Extremadura
region, Spain
. The ancient
structure, which featured flattened arches with a span-to-rise ratio of 4–5:1, is one of the earliest of its kind. Due to its design, it is assumed that the bridge was erected in the early 2nd century AD by the emperors Trajan
or Hadrian
, possibly under the guidance of Apollodorus of Damascus
, the most famous architect of the time.
The almost 300 m long Alconétar Bridge served as a crossing point for the Roman Via de la Plata
, the most important north-south connection in western Hispania
, over the Tagus
, the longest river of the Iberian peninsula
. It presumably remained in service until the Reconquista
, numerous early modern
reconstruction attempts by Spanish engineers failed. The ruins, which were mainly to be found on the right river bank, were relocated from its original position in 1970, when the Alcántara reservoir
was created.
further downstream, spanned the Tagus not far from the mouth of the Almonte
, in the heart of the Spanish Cáceres Province in the Extremadura region. A modern motorway and a railway, which cross the Tagus in the immediate vicinity, underline the historical importance of this crossing point between northern and southern Spain. During the building of the Alcántara Dam in 1970, the remains of the bridge were moved from their original site to a meadow six kilometers to the north, close to the municipality of Garrovillas de Alconétar
. By contrast, few traces are left of the neighbouring ancient bridge over the river Almonte.
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 Alagón, Tiétar and Tagus to the north, then on to the western part of Meseta Central, passing the major town of Salamanca
. Its terminal point was Astorga
in north-western Spain. The Via de la Plata was one of the four main routes which were established by Augustus
(30 BC–14 AD) and his successors for military control of the peninsula and for facilitating the exploitation of the rich Spanish silver and gold mines.
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 Aljucén, a third close to Caparra and a fourth over the Tormes. In the hills overlooking the Alconétar Bridge, a Roman mansio
with the name of Turmulus (Spanish: "Ad Túrmulos") was established, according to the then customary distance intervals. It was the fourth of a total number of sixteen between Mérida and Astorga.
and Trajan is known to have ordered the restoration of the Iter ab Emerita Caesaraugustam when he came to power. Segmental arches were often employed by Trajan's court architect Apollodorus of Damascus, such as in Trajan's Forum
and most notably in the greatest civil engineering achievement of its time, Trajan's Bridge
, which rested on twenty huge concrete piers and was used during the Dacian Wars for moving troops across the more than 1000 m (3,280.8 ft) wide Danube
.
Moorish
geographers make no mention of the Alconétar Bridge, even though they praise the Roman bridge of Alcántara
which also leads across the Tagus. 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-rising bridge of Alcántara. It also remains unknown why the bridge of Alconétar is called Puente de Mantible in the local vernacular, an expression which alludes to the legend of Charlemagne
and his Twelve Paladins.
The bridge was probably in use until the time of the Reconquista, when the Tagus constituted the border between the Christian
and the Moorish realm from the 11th to the 13th century, and the frequent clashes might have easily made the ancient bridge unusable. According to another theory, the water could have begun to wash away the ancient foundations at the time.
The Alconétar Bridge first appears in records in 1231 and, again, in 1257, when it is explicitly referred to as being in use. It was probably repaired by the Knights Templar
who had taken control of the bridge as well as the village in the meantime. The extant arches 1 and 3, both of which are not of Roman fabric, are assumed to date back to this period. Around 1340, however, the bridge was apparently unusable again, so that a ferry service was established to cross the river, which is also recorded at later times. On the site of the ancient way station, a fortress was erected in the Middle Ages
; its tower built of Roman spolia
emerges from the Alcántara reservoir at low water.
Several attempts to reopen the bridge in the early modern era proved unsuccessful. In 1553, the architect Rodrigo Gil de Hontañón
calculated a cost of 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 further 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 large-span segmental arches. The planning sketch shows that already at that time the remaining arches were limited to the right bank, a finding confirmed by the drawing of Fernando Rodríguez from 1797 and engravings in Alexandre de Laborde
s' Voyage pittoresque de l'Espagne a few years later. The reconstruction sketch produced by Rodriguez (see diagram 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, in lieu of the fortification on the right bank viewed upstream, there might have been another segmental arch in Roman times.
The basis for the modern scientific analysis of the bridge was laid out by the civil engineer Antonio Prieto in his 1925 survey, which details the condition of the bridge before its relocation in 1970. Although this was a serious attempt to reconstruct the bridge as close to the original as possible, the Spanish scholar Durán points out that slight changes to the main body can never be avoided in the course of such a difficult undertaking.
The Alconétar Bridge has been classified as "historical heritage" since 1931 by the Spanish authorities.
Main feature of the Alconétar Bridge was the segmental shape of its arches, which were rather uncommon in ancient bridge building: in a survey of Roman bridges in Hispania, only one in ten showed the same characteristics, the vast majority being of semi-circular design. According to Prieto, the bridge had sixteen arch
es, not including the flood openings
on the right approach, with the following spans (estimates are in square brackets):
Other sources however vary from eleven to fifteen arches. The total length of the rectilinear structure was 290 m (951.4 ft), of which 190 m (623.4 ft) spanned the riverbed at low water. If one adds the clear span of the arches and assumes, on the basis of the preserved pier
s, an average pier thickness of 4.4 m (14.4 ft), then the distance between both bridge ramps was 244 m (800.5 ft) (= 178 + 15 x 4.4), which corresponded to a river cross section of 73%. By comparison, the corresponding discharge profiles for the Roman bridges of Córdoba
, of Mérida
and Salamanca
were 62%, 64% and 80% respectively.
Most of the surviving fabric was concentrated on the right bank of the Tagus where the current was less strong; a number of pier stumps rose just above the water surface in the middle of the river, whilst on the left bank a further two piers remained standing, next to which the left abutment
followed. The parts of the bridge moved to a safe place were essentially (see images): the right bridge ramp with its two arch-shaped flood openings, the piers 1, 2, and 3 with the remains of 4 and 6, as well as the vault
s 1 and 3. The other scarce remains were submerged by the flooding of the Alcantara reservoir in 1970.
The approach to the ramp is 42 m (137.8 ft) long and 6.55 metre wide. The clear spans of its two segmental arches are 6.95 m (22.8 ft) and 7.4 m (24.3 ft), which corresponds to a span-to-rise ratio of 4.0 and 3.3 to 1 respectively. The accurately fitting inclined contact surface of the springings clearly proves the Roman origin of these arches. With an extraordinary width of 1.2 m (3.9 ft), the voussoir
s appear oversized in relation to the span (arch slenderness of 1:5.8 and 6.2 respectively). In contrast, the two surviving bridge arches no. 1 and 3 are instable substitutions, made of carelessly laid rubble. The date of these arches is unknown, as with all other repairs; possibly they were built in the period of the Knights Templar.
Equally evidently of post-classical origin is the masonry of the first two piers above the lower cornice
, which projects from all piers at the same height. The superstructure of these piers could have been reconstructed for a drawbridge
or a tower, which, according to an illustration in the Voyage Pittoresque, rested upon pier 2. In contrast, the third pier has still preserved its original Roman character up to the top at 12.5 m (41 ft). Its carefully worked ashlar
and the second cornice, which ran along all ancient piers, provide us with the most distinct impression of the original shape of the Roman bridge.
In particular, it is possible to reconstruct relatively precisely the rise of the Roman segmental arches on the basis of the angles of the inclined stone supports at the springing level. Thus, the third arch originally described a circular sector
of 95°, which points to a span-to-rise ratio of about 4–5 to 1 for the other segmental arches. This value is supported by de Labordes' engravings which depict an intact Roman segmental arch spanning the adjoining fourth bay as late as the early 19th century. Along with other early examples, such as Limyra Bridge
and the Ponte San Lorenzo
, the Alconétar Bridge therefore ranks among the oldest segmental arched bridges in the world. Its existence demonstrates that, in contrast to what had previously been widely believed and taught, Roman bridge builders possessed intimate knowledge of flattened arches.
The pier thicknesses, measuring 4.25 m (13.9 ft), 4.45 m (14.6 ft) and 4.55 m (14.9 ft), increase slightly towards the middle of the river, while the distances between the piers increase from 7.3 m (24 ft) to 10.2 m (33.5 ft). The fifth and ultimate pier, which carries the distinctive nickname "Bishop's table", takes an advanced position in the riverbed and possesses by far the largest cross-section (8.1 m (26.6 ft)). It may be of medieval origin and could have served as a base for a watchtower, replacing two ancient arches. All five piers are strengthened on the upstream face by pointed cutwaters.
The facing of the piers consists of local granite
ashlar, set in parallel courses without the use of mortar
or iron ties (opus quadratum
); their interior, as those of the ramps, was filled with Roman concrete
, a common method applied for Roman bridges. Outwardly, the flattened arches must have lent the bridge a rather elongated appearance, with its roadway following a horizontal or slightly convex line.
Recorded measurements from left to right bank (viewed upstream):
Extremadura
Extremadura is an autonomous community of western Spain whose capital city is Mérida. Its component provinces are Cáceres and Badajoz. It is bordered by Portugal to the west...
region, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
. The ancient
Classical antiquity
Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...
structure, which featured flattened arches with a span-to-rise ratio of 4–5:1, is one of the earliest of its kind. Due to its design, it is assumed that the bridge was erected in the early 2nd century AD by the emperors Trajan
Trajan
Trajan , was Roman Emperor from 98 to 117 AD. Born into a non-patrician family in the province of Hispania Baetica, in Spain Trajan rose to prominence during the reign of emperor Domitian. Serving as a legatus legionis in Hispania Tarraconensis, in Spain, in 89 Trajan supported the emperor against...
or Hadrian
Hadrian
Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...
, possibly under the guidance of Apollodorus of Damascus
Apollodorus of Damascus
Apollodorus of Damascus was a Greek engineer, architect, designer and sculptor who flourished during the 2nd century AD, from Damascus, Roman Syria. He was a favourite of Trajan, for whom he constructed Trajan's Bridge over the Danube for the 105-106 campaign in Dacia. He also designed the Forum...
, the most famous architect of the time.
The almost 300 m long Alconétar Bridge served as a crossing point for the Roman Via de la Plata
Via de la Plata
The Vía de La Plata or Ruta de la Plata is an ancient commercial and pilgrimage path that crosses the west of Spain from north to south, connecting Mérida to Astorga, and in extension Seville with the Bay of Biscay, at Gijón...
, the most important north-south connection in western Hispania
Hispania
Another theory holds that the name derives from Ezpanna, the Basque word for "border" or "edge", thus meaning the farthest area or place. Isidore of Sevilla considered Hispania derived from Hispalis....
, over the Tagus
Tagus
The Tagus is the longest river on the Iberian Peninsula. It is long, in Spain, along the border between Portugal and Spain and in Portugal, where it empties into the Atlantic Ocean at Lisbon. It drains an area of . The Tagus is highly utilized for most of its course...
, the longest river of the Iberian peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
. It presumably remained in service until the Reconquista
Reconquista
The Reconquista was a period of almost 800 years in the Middle Ages during which several Christian kingdoms succeeded in retaking the Muslim-controlled areas of the Iberian Peninsula broadly known as Al-Andalus...
, numerous early modern
Early modern period
In history, the early modern period of modern history follows the late Middle Ages. Although the chronological limits of the period are open to debate, the timeframe spans the period after the late portion of the Middle Ages through the beginning of the Age of Revolutions...
reconstruction attempts by Spanish engineers failed. The ruins, which were mainly to be found on the right river bank, were relocated from its original position in 1970, when the Alcántara reservoir
Alcantara Dam
The Alcantara Dam, also known as the Jose María de Oriol Dam, in Spain, regulates much of the flow of the Tagus River, the longest of the Iberian Peninsula, just before the river enters Portugal. It was built in 1969 and is the second largest reservoir in Europe...
was created.
Location and road access
The historic Alconétar Bridge, which should not be confused with the monumental Alcántara BridgeAlcántara Bridge
The Alcántara Bridge is a Roman stone arch bridge built over the Tagus River at Alcántara, Spain between 104 and 106 CE by an order of the Roman Emperor Trajan in 98...
further downstream, spanned the Tagus not far from the mouth of the Almonte
Almonte (river)
The Almonte is a river in Spain. The 97 km long river is a left tributary of the Tajo, the longest river of the Iberian peninsula. It lies in its entirety in the Extremadura region....
, in the heart of the Spanish Cáceres Province in the Extremadura region. A modern motorway and a railway, which cross the Tagus in the immediate vicinity, underline the historical importance of this crossing point between northern and southern Spain. During the building of the Alcántara Dam in 1970, the remains of the bridge were moved from their original site to a meadow six kilometers to the north, close to the municipality of Garrovillas de Alconétar
Garrovillas de Alconétar
Garrovillas de Alconétar is a municipality located in the province of Cáceres, Extremadura, Spain. According to the 2005 census , the municipality has a population of 2372 inhabitants.Nearby are the remains of the Roman Alconétar Bridge to be found....
. By contrast, few traces are left of the neighbouring ancient bridge over the river Almonte.
In the classical period
Classical antiquity
Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...
, the Alconétar Bridge was part of the Roman road
Roman road
The Roman roads were a vital part of the development of the Roman state, from about 500 BC through the expansion during the Roman Republic and the Roman Empire. Roman roads enabled the Romans to move armies and trade goods and to communicate. The Roman road system spanned more than 400,000 km...
Iter ab Emerita Caesaraugustam
Via de la Plata
The Vía de La Plata or Ruta de la Plata is an ancient commercial and pilgrimage path that crosses the west of Spain from north to south, connecting Mérida to Astorga, and in extension Seville with the Bay of Biscay, at Gijón...
, that was later called Via de la Plata. This important inner Iberian connection led from the provincial capital Mérida
Mérida, Spain
Mérida is the capital of the autonomous community of Extremadura, western central Spain. It has a population of 57,127 . The Archaeological Ensemble of Mérida is a UNESCO World Heritage site since 1993.- Climate :...
in the south, through the river valleys of Alagón, Tiétar and Tagus to the north, then on to the western part of Meseta Central, passing the major town of Salamanca
Salamanca
Salamanca is a city in western Spain, in the community of Castile and León. Because it is known for its beautiful buildings and urban environment, the Old City was declared a UNESCO World Heritage Site in 1988. It is the most important university city in Spain and is known for its contributions to...
. Its terminal point was Astorga
Astorga, Spain
Astorga is a town in the province of León, northern Spain. It lies southwest of the provincial capital of León, and is the head of the council of La Maragatería. The river Tuerto flows through it. , its population was about 12,100 people....
in north-western Spain. The Via de la Plata was one of the four main routes which were established by Augustus
Augustus
Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...
(30 BC–14 AD) and his successors for military control of the peninsula and for facilitating the exploitation of the rich Spanish silver and gold mines.
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 Aljucén, a third close to Caparra and a fourth over the Tormes. In the hills overlooking the Alconétar Bridge, a Roman mansio
Mansio
In the Roman Empire, a mansio was an official stopping place on a Roman road, or via, maintained by the central government for the use of officials and those on official business whilst travelling.-Background:The roads which traversed the Ancient World, were later surveyed,...
with the name of Turmulus (Spanish: "Ad Túrmulos") was established, according to the then customary distance intervals. It was the fourth of a total number of sixteen between Mérida and Astorga.
History
The exact construction date of the Puente de Alconétar is unknown because of missing literary and epigraphic sources. Its segmental arches suggest that it was built in the early 2nd century AD, more specifically during the reign of the emperors Trajan (98–117 AD) or Hadrian (117–138 AD), as the use of this arch form was typical of that era. Both rulers were born in the southern Spanish province of BaeticaHispania Baetica
Hispania Baetica was one of three Imperial Roman provinces in Hispania, . Hispania Baetica was bordered to the west by Lusitania, and to the northeast by Hispania Tarraconensis. Baetica was part of Al-Andalus under the Moors in the 8th century and approximately corresponds to modern Andalucia...
and Trajan is known to have ordered the restoration of the Iter ab Emerita Caesaraugustam when he came to power. Segmental arches were often employed by Trajan's court architect Apollodorus of Damascus, such as in Trajan's Forum
Trajan's Forum
Trajan's Forum is an ancient structure in Rome, Italy, chronologically the last of the Imperial fora. The forum was constructed by the architect Apollodorus of Damascus.-History:...
and most notably in the greatest civil engineering achievement of its time, Trajan's Bridge
Trajan's bridge
Trajan's Bridge or Bridge of Apollodorus over the Danube was a Roman segmental arch bridge, the first to be built over the lower Danube. For more than a thousand years, it was the longest arch bridge in the world, in terms of both total and span length...
, which rested on twenty huge concrete piers and was used during the Dacian Wars for moving troops across the more than 1000 m (3,280.8 ft) wide Danube
Danube
The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....
.
Al-Andalus
Al-Andalus was the Arabic name given to a nation and territorial region also commonly referred to as Moorish Iberia. The name describes parts of the Iberian Peninsula and Septimania governed by Muslims , at various times in the period between 711 and 1492, although the territorial boundaries...
geographers make no mention of the Alconétar Bridge, even though they praise the Roman bridge of Alcántara
Alcántara Bridge
The Alcántara Bridge is a Roman stone arch bridge built over the Tagus River at Alcántara, Spain between 104 and 106 CE by an order of the Roman Emperor Trajan in 98...
which also leads across the Tagus. There is some evidence that a community called Alconétar, Alconétara or Alcontra (Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...
: "small bridge") existed at least temporarily – probably an indirect reference to the high-rising bridge of Alcántara. It also remains unknown why the bridge of Alconétar is called Puente de Mantible in the local vernacular, an expression which alludes to the legend of Charlemagne
Charlemagne
Charlemagne was King of the Franks from 768 and Emperor of the Romans from 800 to his death in 814. He expanded the Frankish kingdom into an empire that incorporated much of Western and Central Europe. During his reign, he conquered Italy and was crowned by Pope Leo III on 25 December 800...
and his Twelve Paladins.
The bridge was probably in use until the time of the Reconquista, when the Tagus constituted the border between the Christian
Christianity
Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...
and the Moorish realm from the 11th to the 13th century, and the frequent clashes might have easily made the ancient bridge unusable. According to another theory, the water could have begun to wash away the ancient foundations at the time.
The Alconétar Bridge first appears in records in 1231 and, again, in 1257, when it is explicitly referred to as being in use. It was probably repaired by the Knights Templar
Knights Templar
The Poor Fellow-Soldiers of Christ and of the Temple of Solomon , commonly known as the Knights Templar, the Order of the Temple or simply as Templars, were among the most famous of the Western Christian military orders...
who had taken control of the bridge as well as the village in the meantime. The extant arches 1 and 3, both of which are not of Roman fabric, are assumed to date back to this period. Around 1340, however, the bridge was apparently unusable again, so that a ferry service was established to cross the river, which is also recorded at later times. On the site of the ancient way station, a fortress was erected in the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...
; its tower built of Roman spolia
Spolia
Spolia is a modern art-historical term used to describe the re-use of earlier building material or decorative sculpture on new monuments...
emerges from the Alcántara reservoir at low water.
Several attempts to reopen the bridge in the early modern era proved unsuccessful. In 1553, the architect Rodrigo Gil de Hontañón
Rodrigo Gil de Hontañón
Rodrigo Gil de Hontañón was a Spanish architect of the Renaissance.He was born at Rascafría. His workings include the Palace of Monterrey in Salamanca, the Palace of Guzmanes in León, and the facade of the Colegio Mayor de San Ildefonso at the University of Alcalá de Henares...
calculated a cost of 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 further 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 large-span segmental arches. The planning sketch shows that already at that time the remaining arches were limited to the right bank, a finding confirmed by the drawing of Fernando Rodríguez from 1797 and engravings in Alexandre de Laborde
Alexandre de Laborde
Comte Louis-Joseph-Alexandre de Laborde was a French antiquary, liberal politician and writer, a member of the Académie des Sciences morales et politiques , under the rubric political economy.-Early years:...
s' Voyage pittoresque de l'Espagne a few years later. The reconstruction sketch produced by Rodriguez (see diagram 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, in lieu of the fortification on the right bank viewed upstream, there might have been another segmental arch in Roman times.
The basis for the modern scientific analysis of the bridge was laid out by the civil engineer Antonio Prieto in his 1925 survey, which details the condition of the bridge before its relocation in 1970. Although this was a serious attempt to reconstruct the bridge as close to the original as possible, the Spanish scholar Durán points out that slight changes to the main body can never be avoided in the course of such a difficult undertaking.
The Alconétar Bridge has been classified as "historical heritage" since 1931 by the Spanish authorities.
Construction
Arch
An arch is a structure that spans a space and supports a load. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.-Technical aspects:The...
es, not including the flood openings
Culvert
A culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...
on the right approach, with the following spans (estimates are in square brackets):
- Meters: 7.30 – 8.20 – 9 – 10.15 – [11 – 12 – 13 – 14 – 15 – 14] – 13 – 12 – 11 – [10] – 9.30 – 9.10
Other sources however vary from eleven to fifteen arches. The total length of the rectilinear structure was 290 m (951.4 ft), of which 190 m (623.4 ft) spanned the riverbed at low water. If one adds the clear span of the arches and assumes, on the basis of the preserved pier
Pier (architecture)
In architecture, a pier is an upright support for a superstructure, such as an arch or bridge. Sections of wall between openings function as piers. The simplest cross section of the pier is square, or rectangular, although other shapes are also common, such as the richly articulated piers of Donato...
s, an average pier thickness of 4.4 m (14.4 ft), then the distance between both bridge ramps was 244 m (800.5 ft) (= 178 + 15 x 4.4), which corresponded to a river cross section of 73%. By comparison, the corresponding discharge profiles for the Roman bridges of Córdoba
Roman bridge of Córdoba
The Roman bridge of Córdoba is a bridge in Córdoba, Andalusia, southern Spain, built in the early 1st century BC across the Guadalquivir river.It is included in the small preserved area known as Sotos de la Albolafia.- History :...
, of Mérida
Puente Romano (Mérida)
The Puente Romano is a Roman bridge over the Guadiana River at Mérida, Spain. It is the longest surviving bridge from ancient times, having once featured an estimated overall length of 755 m with 62 spans. Today, there are 60 spans on a length of 721 m between the abutments...
and Salamanca
Salamanca
Salamanca is a city in western Spain, in the community of Castile and León. Because it is known for its beautiful buildings and urban environment, the Old City was declared a UNESCO World Heritage Site in 1988. It is the most important university city in Spain and is known for its contributions to...
were 62%, 64% and 80% respectively.
Most of the surviving fabric was concentrated on the right bank of the Tagus where the current was less strong; a number of pier stumps rose just above the water surface in the middle of the river, whilst on the left bank a further two piers remained standing, next to which the left abutment
Abutment
An abutment is, generally, the point where two structures or objects meet. This word comes from the verb abut, which means adjoin or having common boundary. An abutment is an engineering term that describes a structure located at the ends of a bridge, where the bridge slab adjoins the approaching...
followed. The parts of the bridge moved to a safe place were essentially (see images): the right bridge ramp with its two arch-shaped flood openings, the piers 1, 2, and 3 with the remains of 4 and 6, as well as the vault
Vault (architecture)
A Vault is an architectural term for an arched form used to provide a space with a ceiling or roof. The parts of a vault exert lateral thrust that require a counter resistance. When vaults are built underground, the ground gives all the resistance required...
s 1 and 3. The other scarce remains were submerged by the flooding of the Alcantara reservoir in 1970.
The approach to the ramp is 42 m (137.8 ft) long and 6.55 metre wide. The clear spans of its two segmental arches are 6.95 m (22.8 ft) and 7.4 m (24.3 ft), which corresponds to a span-to-rise ratio of 4.0 and 3.3 to 1 respectively. The accurately fitting inclined contact surface of the springings clearly proves the Roman origin of these arches. With an extraordinary width of 1.2 m (3.9 ft), the voussoir
Voussoir
A voussoir is a wedge-shaped element, typically a stone, used in building an arch or vault.Although each unit in an arch or vault is a voussoir, two units are of distinct functional importance: the keystone and the springer. The keystone is the center stone or masonry unit at the apex of an arch. A...
s appear oversized in relation to the span (arch slenderness of 1:5.8 and 6.2 respectively). In contrast, the two surviving bridge arches no. 1 and 3 are instable substitutions, made of carelessly laid rubble. The date of these arches is unknown, as with all other repairs; possibly they were built in the period of the Knights Templar.
Equally evidently of post-classical origin is the masonry of the first two piers above the lower cornice
Cornice
Cornice molding is generally any horizontal decorative molding that crowns any building or furniture element: the cornice over a door or window, for instance, or the cornice around the edge of a pedestal. A simple cornice may be formed just with a crown molding.The function of the projecting...
, which projects from all piers at the same height. The superstructure of these piers could have been reconstructed for a drawbridge
Drawbridge
A drawbridge is a type of movable bridge typically associated with the entrance of a castle surrounded by a moat. The term is often used to describe all different types of movable bridges, like bascule bridges and lift bridges.-Castle drawbridges:...
or a tower, which, according to an illustration in the Voyage Pittoresque, rested upon pier 2. In contrast, the third pier has still preserved its original Roman character up to the top at 12.5 m (41 ft). Its carefully worked ashlar
Ashlar
Ashlar is prepared stone work of any type of stone. Masonry using such stones laid in parallel courses is known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry. Ashlar blocks are rectangular cuboid blocks that are masonry sculpted to have square edges...
and the second cornice, which ran along all ancient piers, provide us with the most distinct impression of the original shape of the Roman bridge.
In particular, it is possible to reconstruct relatively precisely the rise of the Roman segmental arches on the basis of the angles of the inclined stone supports at the springing level. Thus, the third arch originally described a circular sector
Circular sector
A circular sector or circle sector, is the portion of a disk enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. In the diagram, θ is the central angle in radians, r the radius of the circle, and L is the arc length of the...
of 95°, which points to a span-to-rise ratio of about 4–5 to 1 for the other segmental arches. This value is supported by de Labordes' engravings which depict an intact Roman segmental arch spanning the adjoining fourth bay as late as the early 19th century. Along with other early examples, such as Limyra Bridge
Limyra Bridge
The Limyra Bridge is a late Roman bridge in Lycia, in modern south-west Turkey, and one of the oldest segmented arch bridges in the world. The long bridge is located near the ancient city of Limyra, and spans the Alakır Çayı river over 26 segmental arches...
and the Ponte San Lorenzo
Ponte San Lorenzo
The Ponte San Lorenzo is a Roman segmental arch bridge over the river Bacchiglione in Padua, Italy. Constructed between 47 and 30 BC, it is one of the very earliest segmental arched bridges in the world...
, the Alconétar Bridge therefore ranks among the oldest segmental arched bridges in the world. Its existence demonstrates that, in contrast to what had previously been widely believed and taught, Roman bridge builders possessed intimate knowledge of flattened arches.
The pier thicknesses, measuring 4.25 m (13.9 ft), 4.45 m (14.6 ft) and 4.55 m (14.9 ft), increase slightly towards the middle of the river, while the distances between the piers increase from 7.3 m (24 ft) to 10.2 m (33.5 ft). The fifth and ultimate pier, which carries the distinctive nickname "Bishop's table", takes an advanced position in the riverbed and possesses by far the largest cross-section (8.1 m (26.6 ft)). It may be of medieval origin and could have served as a base for a watchtower, replacing two ancient arches. All five piers are strengthened on the upstream face by pointed cutwaters.
The facing of the piers consists of local granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
ashlar, set in parallel courses without the use of mortar
Mortar (masonry)
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
or iron ties (opus quadratum
Opus quadratum
Opus quadratum is an ancient Roman construction technique, in which squared blocks of stone of the same height were set in parallel courses, often without the use of mortar.-Technique:...
); their interior, as those of the ramps, was filled with Roman concrete
Roman concrete
Roman concrete was a material used in construction during the late Roman Republic through the whole history of the Roman Empire. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern Portland cement...
, a common method applied for Roman bridges. Outwardly, the flattened arches must have lent the bridge a rather elongated appearance, with its roadway following a horizontal or slightly convex line.
Reconstruction and measurements
| Bridge part | Galiano (ca. 1770) | Rodríguez (1797) | Prieto (1925)Estimated values in italics. | Durán (2004)All values refer to the relocated bridge. |
|---|---|---|---|---|
| Span 1st floodway | 6.86 m (22.5 ft) | 7.04 m (23.1 ft) | 7 m (23 ft) | 6.95 m (22.8 ft) |
| Ramp thickness | 10.6 m (34.8 ft) | 11.63 m (38.2 ft) | 12 m (39.4 ft) | 14 m (45.9 ft) |
| Span 2nd floodway | 7.4 m (24.3 ft) | 7.1 m (23.3 ft) | 7.5 m (24.6 ft) | 7.4 m (24.3 ft) |
| Ramp thickness | 12.9 m (42.3 ft) | 11.65 m (38.2 ft) | 13 m (42.7 ft) | 13.5 m (44.3 ft) |
| Span 1st arch | 7.5 m (24.6 ft) | 7.62 m (25 ft) | 7.3 m (24 ft) | 7.3 m (24 ft) |
| Thickness 1st pier | 5.6 m (18.4 ft) | 4.17 m (13.7 ft) | 4.25 m (13.9 ft) | 4.25 m (13.9 ft) |
| Span 2nd arch | 9 m (29.5 ft) | 8.44 m (27.7 ft) | 8.2 m (26.9 ft) | 8.1 m (26.6 ft) |
| Thickness 2nd pier | 5.6 m (18.4 ft) | 4.19 m (13.7 ft) | 4.25 m (13.9 ft) | 4.45 m (14.6 ft) |
| Span 3rd arch | 9.86 m (32.3 ft) | 8.92 m (29.3 ft) | 8.95 m (29.4 ft) | 8.5 m (27.9 ft) |
| Thickness 3rd pier | 5.5 m (18 ft) | 4.21 m (13.8 ft) | 4.25 m (13.9 ft) | 4.55 m (14.9 ft) |
| Span 4th arch | 10.1 m (33.1 ft) | 10.32 m (33.9 ft) | 10.15 m (33.3 ft) | 10.2 m (33.5 ft) |
| Thickness 4th pier | 4.81 m (15.8 ft) | 4.8 m (15.7 ft) | ||
| Span 5th arch | 12.03 m (39.5 ft) | 11 m (36.1 ft) | ||
| Thickness 5th pier | 6.21 m (20.4 ft) | |||
| Span 6th arch | 16.72 m (54.9 ft) | 12 m (39.4 ft) | ||
| Thickness 6th pier | 6.21 m (20.4 ft) | |||
| Span 7th arch | 8.92 m (29.3 ft) | 13 m (42.7 ft) | ||
| Thickness 7th pier | 6.21 m (20.4 ft) | |||
| Span 8th arch | 16.74 m (54.9 ft) | 14 m (45.9 ft) | ||
| Thickness 8th pier | 6.21 m (20.4 ft) | |||
| Span 9th arch | 11.93 m (39.1 ft) | 15 m (49.2 ft) | ||
| Thickness 9th pier | 4.79 m (15.7 ft) | |||
| Span 10th arch | 10.22 m (33.5 ft) | 14 m (45.9 ft) | ||
| Thickness 10th pier | 4.19 m (13.7 ft) | |||
| Span 11th arch | 8.82 m (28.9 ft) | 13 m (42.7 ft) | ||
| Thickness 11th pier | 4.19 m (13.7 ft) | |||
| Span 12th arch | 8.38 m (27.5 ft) | 12 m (39.4 ft) | ||
| Thickness 12th pier | 4.19 m (13.7 ft) | |||
| Span 13th arch | 11 m (36.1 ft) | |||
| Thickness 13th pier | ||||
| Span 14th arch | 10 m (32.8 ft) | |||
| Thickness 14th pier | ||||
| Span 15th arch | 9.3 m (30.5 ft) | |||
| Thickness 15th pier | ||||
| Span 16th arch | 9.1 m (29.9 ft) | |||