page_title: Alconétar Bridge
section_title: Construction
hierarchical_section_title: Alconétar Bridge / Construction
caption_attribution_description: Deutsch: Grundriss der Reste der römischen Brücke von Alconétar. Abgebildet ist der erhaltene Abschnitt an der rechten Flußseite, der aus der Brückenauffahrt, fünf Pfeilern und vier Bögen besteht. Von links nach rechts: 1 = 1. Entlastungsbogen (römisch) 2 = 2. Entlastungsbogen (römisch) 1 = 1. Brückenbogen (nachantik) 2 = 2. Brückenbogen (zerstört) 3 = 3. Brückenbogen (nachantik) 4 = 4. Brückenbogen (zerstört) 5 = 5. Brückenbogen (zerstört), ursprünglich möglicherweise zwei Bogengewölbe English: Ground plan of the remains of the Roman Alconétar Bridge at the right-hand bank. These include the abutment, five piers and four arches. From left to right: 1 = 1st floodway (Roman) 2 = 2nd floodway (Roman) 1 = 1st bridge arch (post-ancient) 2 = 2nd bridge arch (destroyed) 3 = 3rd bridge arch (post-ancient) 4 = 4th bridge arch (destroyed) 5 = 5th bridge arch (destroyed), orginally possibly two arch vaults Español: Plano de los restos del puente romano de Alconétar
context_page_description: 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, after which 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 their original position in 1970 when the Alcántara reservoir was created.
context_section_description: 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 arches, not including the flood openings 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
  (Feet: 24.0 – 26.9 – 30 – 33.3 – [36 – 39 – 43 – 46 – 49 – 46] – 43 – 39 – 36 – [33] – 30.5 – 29.9.)
  Other sources however vary from eleven to fifteen arches. The total length of the rectilinear structure was 290 m (950 ft), of which 190 m (620 ft) spanned the riverbed at low water. If one adds the clear span of the arches and assumes, on the basis of the preserved piers, an average pier thickness of 4.4 m (14 ft), then the distance between both bridge ramps was 244 m (801 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 vaults 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 (138 ft) long and 6.55–6.80 m (21.5–22.3 ft) wide. The clear spans of its two segmental arches are 6.95 m (22.8 ft) and 7.40 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 1.20 m (3 ft 11 in), the voussoirs 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 12.50 m (41.0 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.
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caption: Ground plan of the extant bridge section
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