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THE ANCIENT PERIOD
Ancient Cantilever Bridges in Asia
BRIDGES of this type are common today in Central Asia, and have been in existence since ancient times. The timber parts, of course, require periodic replacement, but the design has probably remained unchanged for ages.
Plate II shows a bridge in Bhutan, which is of unknown age, but reputed to be very old. The span of this particular bridge is 130 feet. The photograph was taken by John Claude White.
Ancient Chinese Arches
Many fine stone arches are to be found in China; and while little definite data is available regarding them, and especially their ages, enough is known to prove that many of them are perhaps over 2000 years old, although some of those herein illustrated are probably of comparatively recent date, but may be considered as representative of an art that is, in itself, undoubtedly ancient. Some of these structures are beautiful and demonstrate that the Chinese were familiar with many refinements of the art long before these refinements were practiced in Europe. For instance, the projecting extradosal course, which appears first in European bridge architecture about the fifteenth century, was used in an old structure at Chung-King, shown in Plate III.
Has Europe anything that surpasses the simple beauty of the structure at Pu'to'shan, photographed by Ernst Boerschmann and illustrated in his "Picturesque China"? (Plate IV.)
Some of these old Chinese masonry bridges are quite long. Boerschmann shows one comprising fourteen arches, and similar bridges are described in the writings of Marco Polo, who visited China in the thirteenth century A. D. The Chinese have also some interesting bridges of other types than the arch. For instance, there is a bridge of stone slabs on stone piers at Hanchou, the piers decorated with carved heads of animals. (Plate V, Boerschmann.)
There also exist in Eastern Asia good examples of bridges of the timber arch type supported on stone piers, as shown by a bridge in Cashmere, Plate VI, and the suspension type, illustrated by a bridge in Northern Sze-Chuan, built of bamboo cables about eight inches in diameter, Plate VII. In Japan there are many beautiful bridges of timber, most of them utilizing the beam principle, and renewed as required. The rebuilt structure is usually an exact reproduction of the old, thus perpetuating the design, which may be ancient, while the existing structure is recent.
Little is known regarding the ancient bridges of Western Asia. It is supposed that brick arch bridges spanned the Euphrates at Babylon, and a writer asserts that one of these had a span of 660 feet, a statement that seems improbable, and not to be taken seriously.
Some early writers and travelers must have possessed vivid imaginations. George Semple, writing in 1776, describes a stone bridge in China, which he calls the Bridge over the River Saffrany, spanning 600 feet in a single arch, and having a height from its foundation to the top of the parapets of 750 feet and which was known to travelers as the Flying Bridge. It must have flown away.
There are old bridges in Persia, but definite information regarding them is not obtainable. Some were undoubtedly Roman in origin. One at Dizful, over the river Diz, has a length of 1250 feet, contains twenty pointed arches, and is variously dated from 350 B.C. to 300 A.D. Many of these old Persian bridges are built of brick and reflect the influence of Byzantine architecture.
Ancient Pontoon or Floating Bridges
Herodotus tells us that Xerxes built a pontoon bridge over the Hellespont to facilitate his invasion of Greece in the year 480 B.C. According to the noted historian, this bridge was double, consisting of one line of 360 boats and another of 314, the construction being quite similar to the military pontoon bridges of the present day, extensively used in the World War.
Herodotus states that it took the Persians seven days and nights to pass over it, marching in two steady streams. The width of the straits at this point is about a mile, which would correspond to a spacing of the boats of about fifteen feet. Similar bridges are mentioned by Homer, who lived in the ninth century B.C., and Xenophon describes one he built over the Tigris in the "Retreat of the Ten Thousand."
These pontoon bridges belong to the beam type, the stationary piers being replaced by boats or pontoons, which support the ends of the beams that carry the roadway platform. They are crude, requiring but little architectural skill.
While the pontoon type is usually employed for temporary purposes only, some existing structures have served for very long periods, with more or less frequent repairs and rebuilding. One of the most important of such bridges is that over the Golden Horn at Constantinople, recently rebuilt, and illustrated by Plate VIII.
Ancient Pile or Trestle Bridges
The Sublician is supposed to have been the first bridge over the River Tiber constructed by the Romans, and was famous as the bridge defended so heroically by Horatius Codes, who single-handed held the Etruscan army at bay while his comrades destroyed the bridge behind him. As a matter of fact, it was a crude pile and beam structure of timber, the precise details of the construction being a matter of conjecture. Such timber pile bridges are doubtless of ancient origin, as the pre-historic lake dwellers of Europe used a similar construction on which to build their rude huts, which were accessible only by means of a pile and beam bridge connecting with the land, the ancient prototype of the modern timber trestle so familiar to us all.
At one time, about 620 B.C., the Sublician Bridge was rebuilt by the Chief Priests, to whom its maintenance seems to have been entrusted. It is said that they thereupon assumed the title of pontifices, a title which was appropriated and perpetuated by the Christian Church and is supposed to be the origin of the title of the Popes, The Holy Pontiffs.
According to the Encyclopedia Britannica, the word "pontifex" is evidently derived from "pons" (bridge), and "facere," and is believed to have a connection of some kind with the sacred bridge over the Tiber known as the Pons Sublicius, although this is disputed. The Collegium of the Pontifices was the most important priesthood of Rome. The head of the order came to be known, under the Republic, as the Pontifex Maximus, and under the Empire this title was assumed by the Emperors themselves. With the decay of the Empire and rise of the Christian Church to temporal power, this title naturally fell to the Popes. So the highest religious title in Christendom probably is derived from, or is synonymic with, that of the humble bridge builder.
The Pons Sublicius seems never to have been rebuilt in stone, but was always retained as a timber bridge, possibly for sentimental reasons.
Caesar's Bridge over the Rhine
The military bridge which Julius Caesar said he built across the Rhine in ten days' time has been a model for timber pile bridges ever since. The design consisted of pile piers which were protected by ice breakers formed of groups of three piles. These pile piers were capped with rough timbers which supported the lintels or beams, also of rough timbers, and these in turn carried the flooring, a description easily recognized as applying to the typical modern timber trestle bridge. This bridge was about 121/4 meters (40 feet) wide and 425 to 525 meters (1300 to 1600 feet) in length. The individual spans were approximately 61/2 to 8 meters (20 to 25 feet).
The work is thus described in Caesar's Commentaries, the dimensions being given in Roman feet, only slightly different from the modern unit of the same name.
"He joined together at the distance of two feet, two piles each a foot and a half thick, sharpened a little at the lower end, and proportioned in length to the depth of the river. After he had, by means of engines (pile driver or any other machinery), sunk these into the river and fixed them at the bottom, and then driven them in with rammers, not quite perpendicularly like a stake, but bending forward and sloping, so as to incline in the direction of the current of the river; he also placed two other piles opposite to these, at the distance of forty feet lower down, fastened together in the same manner but directed against the force and current of the river. Both these, moreover, were kept firmly apart by beams two feet thick (the space which the binding of the piles occupied), laid in at their extremities between two braces on each side; and in consequence of these being in different directions and fastened on sides the one opposite to the other, so great was the strength of the work, and such the arrangement of the materials, that in proportion as the greater body of water dashed against the bridge, so much the closer were its parts held fastened together. These beams were bound together by timber laid over them in the direction of the length of the bridge and were then covered over with laths and hurdles; and in addition to this, piles were driven into the water obliquely, at the lower side of the bridge, and these serving as buttresses, and being connected with every portion of the work, sustained the force of the stream; and there were others also above the bridge at a moderate distance; that if trunks of trees or vessels were floated down the river by the barbarians for the purpose of destroying the work, the violence of such things might be diminished by these defences, and might not injure the bridge. Within ten days after the timber began to be collected the whole work was completed, and the whole army led over."
Like most military bridges, this famous structure was short lived, being cut down by order of Caesar himself only eighteen days later, having served its purpose. Without doubt, the Roman armies built many such structures.
The pile or trestle bridge, like the pontoon type, admits of but slight architectural treatment, although many such structures have been embellished with more or less artistic timber railings, and, when of rustic design, used for small and light bridges, can be made very attractive.
Trajan's Bridge over the Danube
This was one of the most famous of the early Roman Bridges, and while neither an accurate description nor sufficient ruins for reconstructing it have come down to us, it is known to have consisted of twenty spans of timber arches, supported upon masonry piers, and was therefore the first notable example of the use of this combination. The ruins of thirteen piers are still visible at the site, which is just above the "Iron Gate" of the Danube.
The design is illustrated on the Arch of Trajan at Rome, and attributed to one Apollodorus of Damascus.
This bridge was built by Trajan in order that he might the more readily get at the barbarians to the north of the Danube, and it is of interest, historically, to note that a little later it was demolished by order of the Emperor Hadrian because, it is said, the tables had been turned and the barbarians were using it in order to get back at the Romans. Ancient records state that this project was completed in a single season.
These timber bridges constructed by the Romans were only copies of types that doubtless were common in Europe as well as in Asia for many centuries preceding the Roman era and they therefore belong, historically, to ancient times.
The true Roman Era in bridge building began with the use of the masonry arch, which the Romans developed to a high degree of perfection. Nevertheless, the typical Roman bridge was doubtless always a timber pile trestle, even in the days of the Empire, and, that these structures were not always well built or safe is shown by many references to them in Roman literature, such as the following human quotation from Catullus:
"0, Colonia, you who desire to sport on a long bridge and are prepared to hold your feasts, but you fear the shaky legs of the little bridge standing on second hand sticks, lest it would tumble flat, and lie in the deep marsh. 0, Colonia, give me this gift, of a great laugh, if a good bridge on which the sacred feasts of the Saturnalia might be held is given to you for your games. I wish that a certain fellow townsman of mine might fall from your bridge head over heels into the mud and in truth where the lake and the brimy, stinking swamp is darkest and deepest." Catullus (87-55 B. C.)
It seems strange that the Greeks, who developed an architecture so beautiful and perfect that it has remained the wonder of all succeeding ages, built no bridges worthy of mention. The answer is to be found in the fact that the Greeks built no great highways; they were a sea-faring people and their one great highway was the Mediterranean Sea, on the shores of which they founded their beautiful cities, and over the waters of which they maintained intercity communication.CHAPTER 2
THE ROMAN PERIOD
Roman Bridges over the Tiber at Rome
There are in existence today, wholly or partially intact, six old bridges over the Tiber dating back to Roman times, the Ponte Rotto, the Ponte Sisto, the Ponte Quattro Capi, the Ponte St. Angelo, the Ponte Molle and the Ponte Cestius.
The Ponte Rotto, known to the Romans as the Pons Aemilius (named for the Pontifex Maximum M. Aemilius Lepidus) and to Palladio as the Pons Palatinus, is the most ancient of existing Roman Bridges, but the present ruins of the arches are believed, in the absence of historical records, to be replacements, at least in part, of the original spans. The arches have spans of 24 meters* and the material used was peperino and tufa for the arches, with a facing of travertine. These same materials were used for the other exist- *One meter equals 3.28 feet. ing Roman bridges. (Plate IX.)
The Ponte Sisto as it now exists is believed to have been rebuilt upon the foundations of the old Pons Aurelius or Palatine Bridge by Pope Sixtus IV about 1480, so that probably only parts are Roman. (Plate x.)
The present Ponte Quattro Capi is the ancient Bridge of Fabricius, built in the year 62 B. C. and is practically intact as then built. The modern name is derived from an emblem representing the four-headed Janus, carved on the bridge parapet. The arches have spans of 25 and 34 meters and the width is 15 meters. The structure was repaired in 1680.
The two segmental arches spring from the water level and the spandrel over the center pier is pierced by a large arched opening flanked by two pilasters carried to the coping line. There is a pleasing contrast between the large stones of the arch rings and parapet and the small material used for the spandrel walls. (Plate XI.)
The Ponte St. Angelo is the Pons Aelius of Roman times, built by the Emperor Hadrian in 134 A. D., and consisted of eight arches having a maximum span of 20 meters. The present parapets were added in the seventeenth century and contain ten statues by Bernini, the architect who designed the great Colonnade of St. Peter's. The modern bridge has but five arches admitted to be part of the original construction. These arches have projecting extradosal courses and carefully coursed masonry throughout. (Plate III.)
The Pons Milvius (modern Ponte Molle), located on the Flaminian Way, was built originally in 109 B. C., by M. Aemilius Scaurus, but only parts of the present structure are believed to be the original work. (Plate III.)
The Pons Cestius (modern Ponte St. Bartolomew), built in 43 B. C. and rebuilt about 370 A. D., is in good condition and contains much of the original masonry in spite of numerous restorations. It consists of a single arch.
Roman Bridge at Rimini, Italy
This is a fine example of Roman bridge building and is also noted as being the oldest known bridge built on a skew (with the piers not at right angles with the axis of the bridge). The amount of skew is only 13 degrees and the arch rings are built with horizontal joints. The spans are five in number, from 81/2 to 11 meters in length, supported by piers about 61/2 meters thick.
The material used for the facing is marble and the spandrels are decorated with niches, flanked by pilasters carrying an entablature and pediment. Dentils are also used under the overhanging parapet or coping course. The architectural embellishment is unusual for a Roman bridge, most of them being extremely plain and entirely devoid of applied ornament. This structure was built by the Emperor Augustus in 14 A. D., and is known as the Ponte di Augusto. (Plate XIV.)
The Pont du Gard, Nimes
The Romans required large quantities of water for use in their baths and amphitheatres and as they did not possess the necessary materials to build pipes to resist large internal pressures, they could not use the siphon principle upon which modern engineers rely, and were, therefore, compelled to build numerous huge aqueducts to bring the water to them by gravity. There are many remains of these aqueducts at Rome and in the provinces. One of the best preserved examples is the aqueduct at Nimes in France, attributed to the Emperor Agrippa and to the year 14 A.D., although this is uncertain. The total length of the conduit is 40 kilometers, the aqueduct bridge itself being about 262 meters long and 51.7 meters high.
Excerpted from Great Bridges by Wilbur J. Watson. Copyright © 2006 Dover Publications, Inc.. Excerpted by permission of Dover Publications, Inc..
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