The bridge is 58.2 m high and has a length of 194 m. It consists of six arches "Arco (architecture)"), of unequal height, supported by five pillars that start at different levels. The supports were distributed with distance, so that only two of them penetrate the water of the river, which means that during the dry season the remaining piles are preserved from the erosion of the current, which partly explains the good preservation of the work. These two piles were founded on the slate formations "Slate (rock)") of the river bed, as could be seen when the river bed was diverted to build the Alcántara reservoir dam, which is located a short distance upstream. The pillars are solid bases covered with large padded ashlars, placed with rope and firebrand and with consistent dimensions of 60 × 120 cm. An effect of perfect regularity is created, from which only one course stands out that marks a horizontal line at the bottom of the central piers. The plan of these three central piles is rectangular and triangular cutwaters protrude from them upstream. The two remaining pillars are also rectangular, although with buttresses on both sides.[8]​.

The arches ride on the piers, which are semicircular and with different proportions. Throughout the entire height of the tympanum "Tympanum (architecture)"), on both sides, the buttresses extend in height, a continuity that contributes to highlighting the sense of verticality of a work of great elevation, accentuated by the construction of the 14 m high honorific arch in the middle of the bridge, on the central pillar. This line marks the axis of the bridge's composition.[9] A repeated inscription on both sides of the arch indicates that it was built in honor of the Roman emperor Trajan, born in Hispania. The inscription reads as follows: IMP(eratori)· CAESARI· DIVI· NERVAE· F(ilio)· NERV(ae)/ TRAIANO·AVG(usto)· GERM(anico)· DACICO· PONT(ifici)· MAX(imo)/ TRIB(unicia)· POTES(tate)· VIII· IMP(eratori)· V· CO(n)S(uli)· V· P(atri)· P(atriae). This inscription has the value of setting the date of construction of the bridge between the years 103 and 104 AD. C., in which the ordinals of the emperor's magistracies coincide. We know its content from manuscripts that copied it centuries ago. Originally it was placed on the front of one of the jambs and it is possible that it was complemented by three other inscriptions whose content, although unknown, perhaps extended the list of municipalities or repeated the content of the one that is known.[10] Historian Isaac Moreno Gallo points out that the inscription, being Roman, is not original to the bridge, but was placed in the renovation that was carried out in the century and that comes from somewhere nearby, possibly from the Roman site of Alcántara.[5]​.

The two central arches are the largest, with 28.8 m and 27.4 m span respectively; The collaterals are 21.4 m and the extreme arches are 13.8 m. The symmetry of proportions, therefore, is not absolute in width nor in height, because the irregular terrain to which the work had to be adapted has given different dimensions to the piles, something that however contrasts with the regularity of the design and highlights the horizontality of its deck. The central spans reach the maximum span "Span (engineering)") known in a Roman bridge with the exception of the Bridge of Augustus&action=edit&redlink=1 "Bridge of Augustus (Narni) (not yet written)") in Narni (Italy), with 32 m, which is collapsed and therefore illustrates the danger posed by the overturning of arches of such dimensions. However, the arches of Alcántara have withstood the passage of time and natural erosion, but they have suffered damage from man. Here the ratio of the pier to the arch is somewhat less than a third (3.5), which together with its height provides the bridge with a more diaphanous and lighter profile than the heavy engineering works of Antiquity.[9]​.

At the entrance to the bridge from Alcántara there is a Roman temple made entirely of stone and with a two-slope roof. It has two columns of Tuscan order on the façade and inside there are remains that seem to indicate an ancient internal division into naos and pronaos. Above its door you can read an inscription made in the 17th and 19th centuries based on the original Roman epigraphy and which has the great value of transmitting to us the name of the engineer who directed the construction of the bridge, who also dedicated the temple, Cayo Julio Lacer. The inscription opens with a dedication to the emperor Trajan and then develops an epigram in which he once again alludes to Caesar and the Romulean gods, which begins with the following considerations: «...perhaps the curiosity of travelers, whose care is to know new things, wonders who made it [the bridge] and with what intention. The bridge, destined to last forever in the centuries of the world, was made by Lacer, famous for his divine art...». The phrase may seem pretentious, but the bridge still stands, combining technique and art, renovated several times but preserving the essence of the original work. At the end of the epigram, in a separate line, is his full name (G)aius I(ulius) Lacer, which has not reappeared in any document.[10]​.

It is estimated that the inscription is much later than the Roman work, from around 1480, and that its purpose was, like all the reforms carried out at the time on the bridge by Juan de Zúñiga y Pimentel, to praise the Roman legacy of Spain and unite the reign of the Catholic Monarchs with the Emperor Trajan, of Hispanic origin. The hypothesis defended by the researchers Joan Carbonell") and Helena Jiménez") and supported by the engineer Isaac Moreno Gallo, is that the bridge was built in the times of Augustus (emperor from 27 BC to 14 AD) and that the figure of Cayo Julio Lacer did not exist.[5][6]​.

Middle and Modern Ages

In the century the Muslims founded a small town in its vicinity named Al-Qantarat (القنطرة), "The Bridge", without the need for further nicknames.[1]​ The bridge must have survived intact until the century, when, with the Reconquest of the Christian kingdoms to the south, it suffered the first of several destructions. When King Alfonso IX of León definitively took Alcántara in 1213, the bridge was apparently broken, it is not known whether by Christian or Muslim action. Later, in the successive struggles between Castile and Portugal, Alcántara was an important point of friction. It is documented, as a fact that the consideration of the bridge means, that when the town was surrounded in the time of the Catholic Monarchs, in 1475, King Alfonso V of Portugal raised the fence knowing that Alcántara was going to cut the bridge and sent word to his enemy, Alonso of Aragon, that he would make a detour because "he did not want the kingdom of Castile to keep that building any less."[11]

In 1480 the Order of Alcántara was installed in Alcántara and under the command of Juan de Zúñiga y Pimentel the reform of the bridge was carried out with the purpose of extolling the Romanity of Spain and the monarchy of the Catholic Monarchs, which then dynastically united only the kingdoms of Castile and Aragon. In this reform it is estimated that the central arch, an atypical element in Roman bridges and therefore not original, was built and the commemorative plaques were placed; one of them, the one that refers to the emperor Trajan, possibly brought from the nearby town of Alcántara.[5]​.

The following reconstruction was carried out under the government of King Charles V and these works are well documented. The damage to the factory of the first western arch was repaired, the central arch was crowned with battlements and the bridge was cleaned of military constructions, remains of its strategic importance in medieval wars. The works were carried out by the master Martín López between 1532 and 1543, under the supervision of the architects Pedro de Ibarra and Esteban de Lezcano. To leave a memory of the restoration, the imperial shield was carved that crowns the triumphal arch on the south front and three inscriptions on the jambs where it says: "Charles V Emperor, Caesar Augustus and King of Spain, ordered the repair of this bridge that, deteriorated by wars and its antiquity, threatened ruin, in the year of the Lord 1543, in the 24th of his empire and 26th of his reign." Still in the century, a second intervention was carried out, awarded to Diego de Castañeda and completed by Pedro de Villegas and Sebastián de Aguirre in 1577.[12]​.

In 1707, during the War of Succession, Alcántara was a border point affected in the fights between Spain and Portugal. When the Portuguese withdrew from the town, they tried to blow up the second arch on the right bank without success and the explosion affected the walls of the arch, which partly fell, and the parapets, as well as the core of the factory, which began to show cracks in the honorific arch. The restoration was ordered by Carlos III in 1778.

Contemporary Age

During the War of Independence, to prevent the passage of Napoleonic troops through Alcántara, the allies destroyed the second arch on the right bank in 1809. The absence of this arch was not remedied until 1818 with the installation of a wooden structure for the passage of carriages, but in 1836, during the first Carlist War (1833-1840), it was burned down by Elizabethan troops to prevent the passage of the Carlists led by Miguel Gómez Damas who had invaded the province.[10]​.

Between 1858 and 1860, during the reign of Isabel II, the architect Alejandro Millán Sociats, rebuilt the arch demolished during the War of Independence. The proposal came from the Royal Academy of History, which entrusted the works to the Corps of Civil Engineers, then directed by Alejandro Millán. The arch that had been blown up was rebuilt, the entire factory was consolidated by covering the joints of the ashlars, the honorary arch, which had been dismantled when the collapse of the central pier was feared, was placed in its place, the road was paved and the bridge was complemented with the tracks that exist today at its ends. The reconstruction consists of the commemorative arch inside a tombstone located on the right jamb and a royal shield was also placed at the top of this front. The aforementioned tombstone of Isabel II and another new one that was made on top of the original one, which gave evidence of the Roman municipalities that bordered the bridge, displaced one of the commemorations of Charles I and the only original one that remained there, which were relocated inside the arch. opus iterum bello interruptum, temporis vetustate penis prolapsum restituit aditum utrimque amplificavit, viam latam ad vaccaeos fieri iussit anno domine MDCCCLIX*».

During the reconstruction works, in June 1858, a young man of about nineteen years old named Basilio Borbón, originally from Asturias, drowned after falling into the Tagus River.

It was declared a National Monument on August 13, 1924,[13]

therefore it is an Asset of Cultural Interest "Asset of cultural interest (Spain)") with the category of Monument "Monument (historical heritage of Spain)"),[14]​

and the 90th anniversary of this appointment was commemorated with a human chain.[15]​ In September 1969, to build the Alcántara reservoir, whose dam is 600 meters upstream, the flow of the river was diverted through some tunnels and the channel was completely dry for several kilometers. It was then observed that one of the bridge piers was loosening, and it was repaired.

The bridge was chosen "Best Corner in Spain" in 2014 in a popular vote contest organized by the Repsol Guide.[16]​ In 2019 the Assembly of Extremadura asked to promote its declaration as a World Heritage Site, carry out restoration work and build a new bridge to eliminate the traffic of some 237,000 vehicles that annually crossed the Roman engineering work.[17]​ The new Alcántara bridge was inaugurated on October 20, 2025, and its entry into operation finally freed the Roman bridge from the road traffic it supported.[18]​.

The Roman bridge of Alcántara is located about 400 m north of the town of the same name, on the road that leads to Portugal, crossing the path over the Tagus River. Formerly it was part of the Norba road that communicated with the Portuguese north, linking the intermediate area of ​​Beira Alta with two important arteries, the Silver road and the Lisbon to Braga road. It was a secondary road in the network of Roman roads in Hispania, which is why the superb bridge was not a public work sponsored by the Roman State, although it was a region well regarded for its metal deposits.[4] Likewise, in Ancient Rome the bridge works (opus pontis) were the responsibility of the nearby municipium and the fact of sharing the costs meant that the infrastructure belonged to the entire region and not to a single municipality. The mission of this infrastructure was, therefore, to connect the area north of the Tagus with the southern region, and there were twelve localities, whose names appear in an inscription, that paid for the works.[7]​[1]​.

The place chosen to cross the riverbed of the Tagus is a section that has a natural narrowing between two bends that reduce the force of its flow. On the other hand, before the construction of the Alcántara reservoir dam in the middle of the century, the water levels in this natural canyon reached high heights that forced the construction of an unusually high engineering work.[1]​.

The bridge is 58.2 m high and has a length of 194 m. It consists of six arches "Arco (architecture)"), of unequal height, supported by five pillars that start at different levels. The supports were distributed with distance, so that only two of them penetrate the water of the river, which means that during the dry season the remaining piles are preserved from the erosion of the current, which partly explains the good preservation of the work. These two piles were founded on the slate formations "Slate (rock)") of the river bed, as could be seen when the river bed was diverted to build the Alcántara reservoir dam, which is located a short distance upstream. The pillars are solid bases covered with large padded ashlars, placed with rope and firebrand and with consistent dimensions of 60 × 120 cm. An effect of perfect regularity is created, from which only one course stands out that marks a horizontal line at the bottom of the central piers. The plan of these three central piles is rectangular and triangular cutwaters protrude from them upstream. The two remaining pillars are also rectangular, although with buttresses on both sides.[8]​.

The arches ride on the piers, which are semicircular and with different proportions. Throughout the entire height of the tympanum "Tympanum (architecture)"), on both sides, the buttresses extend in height, a continuity that contributes to highlighting the sense of verticality of a work of great elevation, accentuated by the construction of the 14 m high honorific arch in the middle of the bridge, on the central pillar. This line marks the axis of the bridge's composition.[9] A repeated inscription on both sides of the arch indicates that it was built in honor of the Roman emperor Trajan, born in Hispania. The inscription reads as follows: IMP(eratori)· CAESARI· DIVI· NERVAE· F(ilio)· NERV(ae)/ TRAIANO·AVG(usto)· GERM(anico)· DACICO· PONT(ifici)· MAX(imo)/ TRIB(unicia)· POTES(tate)· VIII· IMP(eratori)· V· CO(n)S(uli)· V· P(atri)· P(atriae). This inscription has the value of setting the date of construction of the bridge between the years 103 and 104 AD. C., in which the ordinals of the emperor's magistracies coincide. We know its content from manuscripts that copied it centuries ago. Originally it was placed on the front of one of the jambs and it is possible that it was complemented by three other inscriptions whose content, although unknown, perhaps extended the list of municipalities or repeated the content of the one that is known.[10] Historian Isaac Moreno Gallo points out that the inscription, being Roman, is not original to the bridge, but was placed in the renovation that was carried out in the century and that comes from somewhere nearby, possibly from the Roman site of Alcántara.[5]​.

The two central arches are the largest, with 28.8 m and 27.4 m span respectively; The collaterals are 21.4 m and the extreme arches are 13.8 m. The symmetry of proportions, therefore, is not absolute in width nor in height, because the irregular terrain to which the work had to be adapted has given different dimensions to the piles, something that however contrasts with the regularity of the design and highlights the horizontality of its deck. The central spans reach the maximum span "Span (engineering)") known in a Roman bridge with the exception of the Bridge of Augustus&action=edit&redlink=1 "Bridge of Augustus (Narni) (not yet written)") in Narni (Italy), with 32 m, which is collapsed and therefore illustrates the danger posed by the overturning of arches of such dimensions. However, the arches of Alcántara have withstood the passage of time and natural erosion, but they have suffered damage from man. Here the ratio of the pier to the arch is somewhat less than a third (3.5), which together with its height provides the bridge with a more diaphanous and lighter profile than the heavy engineering works of Antiquity.[9]​.

At the entrance to the bridge from Alcántara there is a Roman temple made entirely of stone and with a two-slope roof. It has two columns of Tuscan order on the façade and inside there are remains that seem to indicate an ancient internal division into naos and pronaos. Above its door you can read an inscription made in the 17th and 19th centuries based on the original Roman epigraphy and which has the great value of transmitting to us the name of the engineer who directed the construction of the bridge, who also dedicated the temple, Cayo Julio Lacer. The inscription opens with a dedication to the emperor Trajan and then develops an epigram in which he once again alludes to Caesar and the Romulean gods, which begins with the following considerations: «...perhaps the curiosity of travelers, whose care is to know new things, wonders who made it [the bridge] and with what intention. The bridge, destined to last forever in the centuries of the world, was made by Lacer, famous for his divine art...». The phrase may seem pretentious, but the bridge still stands, combining technique and art, renovated several times but preserving the essence of the original work. At the end of the epigram, in a separate line, is his full name (G)aius I(ulius) Lacer, which has not reappeared in any document.[10]​.

It is estimated that the inscription is much later than the Roman work, from around 1480, and that its purpose was, like all the reforms carried out at the time on the bridge by Juan de Zúñiga y Pimentel, to praise the Roman legacy of Spain and unite the reign of the Catholic Monarchs with the Emperor Trajan, of Hispanic origin. The hypothesis defended by the researchers Joan Carbonell") and Helena Jiménez") and supported by the engineer Isaac Moreno Gallo, is that the bridge was built in the times of Augustus (emperor from 27 BC to 14 AD) and that the figure of Cayo Julio Lacer did not exist.[5][6]​.

Middle and Modern Ages

In the century the Muslims founded a small town in its vicinity named Al-Qantarat (القنطرة), "The Bridge", without the need for further nicknames.[1]​ The bridge must have survived intact until the century, when, with the Reconquest of the Christian kingdoms to the south, it suffered the first of several destructions. When King Alfonso IX of León definitively took Alcántara in 1213, the bridge was apparently broken, it is not known whether by Christian or Muslim action. Later, in the successive struggles between Castile and Portugal, Alcántara was an important point of friction. It is documented, as a fact that the consideration of the bridge means, that when the town was surrounded in the time of the Catholic Monarchs, in 1475, King Alfonso V of Portugal raised the fence knowing that Alcántara was going to cut the bridge and sent word to his enemy, Alonso of Aragon, that he would make a detour because "he did not want the kingdom of Castile to keep that building any less."[11]

In 1480 the Order of Alcántara was installed in Alcántara and under the command of Juan de Zúñiga y Pimentel the reform of the bridge was carried out with the purpose of extolling the Romanity of Spain and the monarchy of the Catholic Monarchs, which then dynastically united only the kingdoms of Castile and Aragon. In this reform it is estimated that the central arch, an atypical element in Roman bridges and therefore not original, was built and the commemorative plaques were placed; one of them, the one that refers to the emperor Trajan, possibly brought from the nearby town of Alcántara.[5]​.

The following reconstruction was carried out under the government of King Charles V and these works are well documented. The damage to the factory of the first western arch was repaired, the central arch was crowned with battlements and the bridge was cleaned of military constructions, remains of its strategic importance in medieval wars. The works were carried out by the master Martín López between 1532 and 1543, under the supervision of the architects Pedro de Ibarra and Esteban de Lezcano. To leave a memory of the restoration, the imperial shield was carved that crowns the triumphal arch on the south front and three inscriptions on the jambs where it says: "Charles V Emperor, Caesar Augustus and King of Spain, ordered the repair of this bridge that, deteriorated by wars and its antiquity, threatened ruin, in the year of the Lord 1543, in the 24th of his empire and 26th of his reign." Still in the century, a second intervention was carried out, awarded to Diego de Castañeda and completed by Pedro de Villegas and Sebastián de Aguirre in 1577.[12]​.

In 1707, during the War of Succession, Alcántara was a border point affected in the fights between Spain and Portugal. When the Portuguese withdrew from the town, they tried to blow up the second arch on the right bank without success and the explosion affected the walls of the arch, which partly fell, and the parapets, as well as the core of the factory, which began to show cracks in the honorific arch. The restoration was ordered by Carlos III in 1778.

Contemporary Age

During the War of Independence, to prevent the passage of Napoleonic troops through Alcántara, the allies destroyed the second arch on the right bank in 1809. The absence of this arch was not remedied until 1818 with the installation of a wooden structure for the passage of carriages, but in 1836, during the first Carlist War (1833-1840), it was burned down by Elizabethan troops to prevent the passage of the Carlists led by Miguel Gómez Damas who had invaded the province.[10]​.

Between 1858 and 1860, during the reign of Isabel II, the architect Alejandro Millán Sociats, rebuilt the arch demolished during the War of Independence. The proposal came from the Royal Academy of History, which entrusted the works to the Corps of Civil Engineers, then directed by Alejandro Millán. The arch that had been blown up was rebuilt, the entire factory was consolidated by covering the joints of the ashlars, the honorary arch, which had been dismantled when the collapse of the central pier was feared, was placed in its place, the road was paved and the bridge was complemented with the tracks that exist today at its ends. The reconstruction consists of the commemorative arch inside a tombstone located on the right jamb and a royal shield was also placed at the top of this front. The aforementioned tombstone of Isabel II and another new one that was made on top of the original one, which gave evidence of the Roman municipalities that bordered the bridge, displaced one of the commemorations of Charles I and the only original one that remained there, which were relocated inside the arch. opus iterum bello interruptum, temporis vetustate penis prolapsum restituit aditum utrimque amplificavit, viam latam ad vaccaeos fieri iussit anno domine MDCCCLIX*».

During the reconstruction works, in June 1858, a young man of about nineteen years old named Basilio Borbón, originally from Asturias, drowned after falling into the Tagus River.

It was declared a National Monument on August 13, 1924,[13]

therefore it is an Asset of Cultural Interest "Asset of cultural interest (Spain)") with the category of Monument "Monument (historical heritage of Spain)"),[14]​

and the 90th anniversary of this appointment was commemorated with a human chain.[15]​ In September 1969, to build the Alcántara reservoir, whose dam is 600 meters upstream, the flow of the river was diverted through some tunnels and the channel was completely dry for several kilometers. It was then observed that one of the bridge piers was loosening, and it was repaired.

The bridge was chosen "Best Corner in Spain" in 2014 in a popular vote contest organized by the Repsol Guide.[16]​ In 2019 the Assembly of Extremadura asked to promote its declaration as a World Heritage Site, carry out restoration work and build a new bridge to eliminate the traffic of some 237,000 vehicles that annually crossed the Roman engineering work.[17]​ The new Alcántara bridge was inaugurated on October 20, 2025, and its entry into operation finally freed the Roman bridge from the road traffic it supported.[18]​.