Bridges

The highest bridge over the water or ground was the single-arched Pont d'Apl which carried irrigation water for Aosta across a deep Alpine gorge. The height of its deck over the torrent below measures 66 m.
The largest pointed arch bridge by span was the Karamagara Bridge in Cappadocia with a clear span of 17 m. Constructed in the 5th or 6th century AD across a tributary of the Euphrates, the now submerged structure is one if the earliest known examples of pointed architecture in late antiquity, and may even be the oldest surviving pointed arch bridge.
The largest rivers to be spanned by solid bridges were the Danube and the Rhine, the two largest European rivers west of the Eurasian Steppe. The lower Danube was crossed at least at two different crossing points (Drobeta-Turnu Severin, Corabia), while the middle and lower Rhine at four (Mainz, Neuwied, Koblenz, Cologne). For rivers with strong currents and to allow swift army movements, pontoon bridges were also routinely employed. Going from the distinct lack of records of solid bridges spanning larger rivers elsewhere, the Roman feat appears to be unsurpassed anywhere in the world until well into the 19th century.
The longest bridge, and one of the longest of all time, was Constantine's Bridge with an overall length of 2437 m, 1137 m of which crossed the Danube's riverbed.
The second longest bridge was the monumental Trajan's Bridge which was situated further upstream from Constantine's. It was a record-holder in various categories, such as the largest bridge by span and the longest segmental arch bridge. Erected 104–105 AD by the engineer Apollodorus of Damascus for facilitating the advance of Roman troops in the Dacian Wars, it featured twenty-one spans covering a total distance of between 1070 and 1100 m. These twenty-one wooden arches spanned 50 m each from centreline to centreline. Its wooden superstructure was supported by twenty concrete piers.
The longest existing Roman bridge is the sixty-two span Puente Romano at Mèrida, Spain (today 790 m).
The total length of all aqueduct arch bridges of the Aqua Marcia to Rome, constructed from 144 to 140 BC, amounts to 10 km.
Pont Serme in southern France reached a length of 1500 m, but may be better classified as an arcaded viaduct.
The Bridge at Limyra in modern-day Turkey, consisting of twenty-six flat brick arches, features the greatest lengths of all extant masonry structures in this category (360 m).
The tallest bridge was the Pont du Gard, which carried water across the Gard river to Nоmes, southern France. The 270 m long aqueduct bridge was constructed in three tiers which measure successively 20.5 m, 19.5 m and 7.4 m, adding up to a total height of 47.4 m above the water-level. When crossing deeper valleys, Roman hydraulic engineers, for reasons of relative economics, preferred inverted siphons over bridges; this is evident in the Lyon aqueduct where seven out of nine siphons exceed the 45 m mark, reaching depths up to 123 m. The tallest road bridges were the monumental Alcбntara Bridge, Spain (ca. 42 m), and the bridge at Narni (30 m).

The widest bridge was the Pergamon Bridge in Pergamon, Turkey. The structure served as a substruction for a large court in front of the Serapis Temple, allowing the waters of the Selinus river to pass unrestricted underneath. Measuring 193 m in width, the dimensions of the extant bridge are such that it is frequently mistaken for a tunnel, although the whole structure was actually erected above ground. A similar design was also executed in the Nysa Bridge which straddled the local stream on a length of 100 m, supporting a forecourt of the city theatre. By comparison, the width of a normal, free standing Roman bridge did not exceed 10 m.

Load capacity plus ratio of clear span against rise, arch rib and pier thickness:

The bridge with the greatest load capacity – as far as can be determined from the limited research – was the Alcàntara Bridge the largest arch of which can support a load of 52 t, followed by the Ponte de Pedra (30 t), Puente Bibei (24 t) and Puente de Ponte do Lima (24 t) (all in Hispania). According to modern calculations, the Limyra Bridge, Asia Minor, can support a 30 t vehicle on one arch plus a load of 500 kp/mІ on the remaining surface of the arch. The load limit of Roman arch bridges was thus far in excess of the live loads imposed by ancient traffic.
The bridge with the flattest arches was the Trajan's Bridge, with a span-to-rise ratio of about 7 to 1. It also held several other important architectural records (see below). A number of fully-stone segmental arch bridges, scattered throughout the empire, featured ratios of between 6.4 and 3.0, such as the relatively unknown Bridge at Limyra, the Ponte San Lorenzo and the Alcontar Bridge. By comparison, the Florentine Ponte Vecchio, one of the earliest segmental arch bridges in the Middle Ages, features a ratio of 5.3 to 1.
The bridge with the most slender arch was the Pont-Saint-Martin in the Alpine Aosta Valley. A favourable ratio of arch rib thickness to span is regarded as the single most important parameter in the design of stone arches. The arch rib of the Pont-Saint-Martin is only 1.03 m thick what translates to a ratio of 1/34 respectively 1/30 depending on whether one assumes 35.64 m or 31.4 m to be the value for its clear span. A statistical analysis of extant Roman bridges shows that ancient bridge builders preferred a ratio for rib thickness to span of 1/10 for smaller bridges, while they reduced this to as low as 1/20 for larger spans in order to relieve the arch from its own weight.
The bridge with the most slender piers was the three-span Ponte San Lorenzo in Padua, Italy. A favourable ratio between pier thickness and span is considered a particularly important parameter in bridge building, since wide openings reduce stream velocities which tend to undermine the foundations and cause collapse. The approximately 1.70 m thick piers of the Ponte San Lorenzo are as slender as one-eighth of the span. In some Roman bridges, the ratio still reached one-fifth, but a common pier thickness was around one third of the span. Having been completed sometime between 47 and 30 BC, the San Lorenzo Bridge also represents one of the earliest segmental arch bridges in the world with a span to rise ratio of 3.7 to 1.

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