The bridges built in southern France were particularly fine. The bridge at Espalion is re garded as the oldest—built in 780—and it was probably the first with the pointed arch. The Saint Esprit.the Beziers, the Montauban and the Pont Valentre, over the Lot at Cahors, are some of the best examples of those built dur ing the period covered by the later part of the 13th and the earlier part of the 14th centuries. The application of the system of end and central towers for purposes of fortifications received the highest development at this time. This was especially true in France where the mediaeval social conditions made such forti fications an absolute necessity. In this respect, Germany and Spain were far behind France, although the monumental bridge of 15 semi circular arches across the Danube at Ratisbon, built by the Germans in 1135, and the bridge of 18 semi-circular arches across the Elbe at Dres den, were very fine examples of this kind. The Spanish bridges at Zamora, Tudela, Lograno, and Palencia, built during the period 1135 to 1192, are of the pointed arch type, some of them consisting of as many as 20 arches.
Of the Italian bridges built during this period, the best examples are the Ponte Vecchio in Florence, originally built in 1177 and re built in 1362, the bridge at Mantua, and the Rialto Bridge over the Grand Canal in Venice, built in 1588. These bridges were of the covered type, that is, they had a covered gallery which was flanked by a double line of booths and small shops in which all kinds of merchandise were exposed for sale. In Italy, the use of wood as a material of construction was gener ally adhered to until the 13th century, although in France, and in the other countries of north ern Europe it had been generally supplanted by masonry. Yet, at the close of the 15th century, Italy had some fine stone structures the bridges at Mossa and Signa in Tuscany, and the Ponte del Diavolo near Lucca, with one span of 120 feet ; while France had many large wooden bridges at several important points.
The engineers of the Renaissance returned to the round arch typical of the Roman bridges, but they showed great boldness in their designs, by increasing the span of the arches. The bridge across the Adda at Trezzo, built under the orders of Bernabo Visconti, Duke of Milan, during the latter part of the 14th century, con sisted of a single arch of granite with a span of 251 feet, and a radius of 133 feet, while the bridge over the Ticino at Pavia consisted of seven pointed arches of brick work, each 70 feet in span and 64 feet rise.
Of the smaller Italian bridges, the most famous is the Bridge of Sighs at Venice, built during the latter part of the 16th century, to connect the Ducal Palace with the prison.
In England, the use of stone as a material of bridge construction dates back to the bridge over the East Dart at Dartmoor, believed to be over 2,000 years old. A stone bridge at Bow over the river Lea is the earliest English bridge of that type of which there are records. It was built about 1110. An old bridge over the Thames was in existence in 978, and in some records of 1014 there is mention of another. By existing records it appears that a triangular pointed arch stone bridge at Croyland, Lincoln shire, was chartered in 943. The present
structure, known as the Croyland Bridge, how ever, although one of the oldest stone bridges in England, appears to have been built about the latter part of the 14th century. It is also triangular in form, and consists of three pointed arches which span the waters of the Welland, the Nyne and the Catwater drain. On account of its steep grade it can be used only by foot passengers.
The work of the oBrethren of the order carried the art of bridge-building up to the 17th century, and a great many fine struc tures were built in all parts of Europe. In France, the mdst important were the Trilpot, Tours, Gignac, Neuilly and Blois bridges, and in England, the Blackfriars, Westminster, Wins ton and Kelso. The date of the building of the first London bridge across the Thames is quite uncertain; but, there is very little doubt that it was built of timber and had to be frequently reconstructed. The so-called great London Bridge was built of stone, between the years 1176 and 1209, by an architect sent from France for that purpose. It had a covered gallery which was lined on both sides by shops, like a regular street. It consisted of 19 or 20 pointed arches, varying from 20 feet to 9 feet in span, and had a total length of 940 feet. It was supplanted by the structure now known as °Old London Bridge," in 1831. This structure con sists of five elliptical arches, of which the centre arch has a span of 152 feet, with a height of 291/2 feet above high-water mark. The two next are 140 feet, and the two shore arches 130 feet in span, with a height of feet. The total length of the structure is 1,005 feet, and it carries a roadway 53 feet wide between the parapets. The Blackfriars Bridge across the Thames was built between the years 1760 and 1768. It comprised nine elliptical arches. The central arch had a span of 100 feet, and the others decreased gradually from 98 feet in those next to the centre, to 70 feet in those at the ends. This bridge was replaced in 1865 by a cast-iron bridge of five spans. The Westmin ster Bridge was built between the years 1738 and 1750. It consists of 15 semi-circular arches, of which the centre arch is 76 feet in span, and the span of the others decreases at the rate of four feet for each succeeding arch, except the two shore arches, each of which has a span of 25 feet. It is 1,164 feet long. Other notable English stone bridges built during the 18th century are the Winston Bridge over the river Tees, and the Kelso Bridge over the Tweed. The former has a superb arch 109 feet in span, while the latter consists of five arches, each of which are 72 feet in span. Perhaps the most notable stone arch bridge built in any country during the 18th century is the Pont-y Prydd, across the river Taff in Wales. It was built by William Edwards, a clergyman, after ward a stone mason, in 1750, after two failures due to excessive weight of the haunches, which in the third and successful attempt were light ened by the introduction of pierced spandrels. It consists of a segmented arch 150 feet in span, with a height of 35 feet, and its most curious feature is the gradual increase of its width by offsets, from 141/2 feet at the crown of the arch to 16 feet at the abutments.