The most remarkable bridges constructed in France during the 18th century were the work of the famous Department of Ponts et Chaus sees, established in 1715. The best examples of their work are the Blois Bridge over the Loire, the construction of which was com menced in 1720, and which consists of 11 ellip tical arches, ranging from about 55 feet to 68 feet in span; the bridge over the Loire at Tours, the construction of which was com menced in 1755, and which consists of 15 ellipti cal arches, each 80 feet in span, and separated by piers 16 feet thick; the Trilport Bridge over the Marne, built in 1760, consisting of three skew arches, the middle arch of which has a span of 81 feet, and the side arches, spans of about 77 feet; the Neuilly Bridge across the Seine, built between the years 1768 and 1774, and which consists of five elliptical arches, each 128 feet in span; and the Gignac Bridge over the Herault, built in 1793, and which consists of an elliptical centre arch 161 feet in span, flanked by two semi-circular arches, each of which have a span of 72 feet.
Although the masonry and stone arch bridges of the 19th century cannot be considered as showing much, if any, structural improvement over those of preceding times, it is a fact that the engineers of the 19th century used their better knowledge of the theory of those struc tures, obtained from the progress of the science of statics, to increase the spans of the arches far beyond the limits set by the earlier practice.
Of these later productions, the largest stone arch in the world at the time was that of the Luxemburg Bridge, completed in 1901; it is 277 feet in span, with a rise of 102 feet and a clear height of about 138 feet above the level of the water. It is surpassed in span by the Plauen Bridge which crosses the valley of the Syra, a flat elliptical arch 295 feet in span with 58 feet rise, and a width of 56 feet. Other modern stone arches of magnitude are the Grosvenor Bridge over the river Dee at Chester, the largest span in England, consisting of a single arch with.a span of 200 feet, and the Waterloo Bridge across the Thames, of nine elliptical arches of Aberdeen granite, of 120 feet span each, with a rise of 34 feet. The total length of the structure, including the approaches, is 2,456 feet, and it carries a horizontal roadway 41% feet wide between the parapets.
In America the earliest notable stone bridge structure was the Tempoalo aqueduct near Huauchinango, Mexico, built between 1553 and 1570. It consists of 68 semi-circular arches, the largest span being 58 feet. Its maximum
height was 124 feet. Another Mexican stone aqueduct bridge of note was a part of the water supply system of the city of Queretaro, built by the Spaniards between 1726 and 1735. It has 74 spans of 50 feet each, and a maximum height of 92 feet.
The earliest stone bridge in the United States of which there is definite record was that at Ipswich, Mass. It .has two spans of 28 feet each. The Rochester aqueduct begun in 1820, and the Washington aqueduct (over the Po tomac) begun in 1837 were the first important stone bridges in the country. High Bridge, carrying the Croton aqueduct across the Harlem River, surpassed all previous constructions. This bridge has 15 arches, the eight crossing the water being 80 feet wide, and the seven land spans being 50 feet wide. The height in the clear is 100 feet above high water, and the parapet is 116 feet above the same level. Its total length is 1,460 feet. It was built between 1837 and 1842. Cabin John Bridge, carrying the Washington (city) aqueduct, was built between 1857 and 1864. It is a single arch of 220 feet span — and a 110-degree segment of a circle whose radius is 134 feet. The rise of the arch is 57 feet. For many years it was the longest stone arch in the world.
Beginning with 1835, many of the early wooden railroad bridges in the United States have been replaced by bridges. The first was the Carrollton Viaduct,.carrying the West ern Maryland Railroad across the Patapsco Creek. In 1847 the Starucca Viaduct was built to carry the Erie Railroad over the Starucca Creek. This was of sandstone, in 17 flat arches of 51 feet span, 1,200 feet long, and the floor 110 feet above the creek. At first it accommo dated only a single track, but it was afterward doubled on the original plan, for a second track. In 1881 a stone-arch viaduct of five 70-foot spans was built for the Philadelphia and Reading Railroad over Wissahickon Creek, and a similar bridge for the Lake Shore and Michigan Southern Railroad over the Grand River at Painesville, Ohio. In 1881 a stone-arch bridge notable for its length was begun over the Mississippi River at Minneapolis. It was of 22 spans, four of which were 100 feet, fif teen of 80 feet, and one each of 71 feet, 43 feet and 40 feet. It carried union tracks at a height of 65 feet above the water. In 1888 the Pennsylvania Railroad Company began to re place its wooden and iron bridges with more permanent structures of stone and concrete, and some of these are of notable dimensions.