the Delaware at Trenton, which took three years to build (1804–6), closely resembles the Wettingen bridge. Engravings of both Swiss bridges clearly showed them to have been covered with roofs. From references in several documents, we know that a few Americans knew the European tradition of covering wooden bridges for protection.
Andrea Palladio included plans for three truss bridges in his 1570 I quattro libri dell’architettura [The Four Books of Architecture], two reproduced here: (left) 1–15, a queenpost design, and (right) 1–16, a multiple kingpost design. (Palladio, English translation, 1738)
Now long gone, Schaffhausen, Switzerland’s famous bridge over the Rhine, was much noted by travelers and artists, here immortalized in the hand-colored etching by Johann Heinrich Bleuler (1758–1823). The 364-foot two-span bridge was built between 1756 and 1758 by Hans Ulrich Grubenmann, whose complex design involving numerous polygonal arches and various struts attracted the attention of early civil engineers. (© Trustees of the British Museum)
Although there is the possibility that America’s self-made bridge builders could have known the work of Palladio and the Grubenmann families, there is no known direct evidence to connect them to those specific designs or bridges. What is so remarkable about the nation’s first generation of bridge engineers is that they not only, as it were, had to “reinvent the wheel” but did it with an unparalleled boldness bordering on the brazen. Civil engineering historian Lee H. Nelson’s concise but definitive study, The Colossus of 1812: An American Engineering Superlative (1990), focuses on the work of four exemplary early builders and their bridges: Charles Willson Peale (1741–1827), Timothy Palmer (1751–1821), Theodore Burr (1771–1822), and Lewis Wernwag (1769–1843).
Among the first problems encountered by early bridge builders was that many of the young American towns needing bridges sat beside broad tidal rivers which often flowed deep. Some were more than a thousand feet wide, others even half a mile, and in one case, the Susquehanna in central Pennsylvania, more than a mile wide at some points. All were major impediments to transportation, trade, and urban expansion. Frances Manwaring Caulkins’ History of Norwich, Connecticut sums it up well: “. . . roads could not have been opened and rendered safe for traveling in any direction without spanning a multitude of small streams with some kind of stone-work, or with timber and plank, and these perhaps the next spring flood would sweep away. Consequently the work of building and repairing bridges was always beginning, ever going on, and never completed” (1874: 343).
Partial plan of Schaffhausen Bridge showing both trusses and cross sections. (Fletcher and Snow, 1934)
Until the French developed deep-water caisson technology during the nineteenth century, builders of multiple-span bridges had to contend with the difficult task of placing stone piers mid river, sometimes utilizing simple coffer dams, which were temporary enclosures within a stream. It was not until 1872 that James B. Eads, the builder of the Brooklyn Bridge, took out his path-breaking patent for a watertight caisson structure that greatly facilitated the construction of deep-water bridge piers. Until then, builders were only able to construct piers in relatively shallow rivers and consequently were forced into creating (or at least imagining) grandiose spans for other situations. Some early builders proposed and even built some of the most daring bridges in American history.
Thomas Pope patented his “Flying Pendent Lever Bridge” in 1807 and published plans in his 1811 A Treatise on Bridge Architecture. There he claimed (imagined) that he could build an 1,800-foot covered arch over the East River in New York City. (American Philosophical Society)
Charles Willson Peale published his proposal for a 390-foot laminated arch bridge over the Schuylkill at Market Street in Philadelphia in An Essay on Building Wooden Bridges. (Peale, 1797; reproduced in Nelson, 1990: 7)
To get an idea of their boldness, consider New York “architect and landscape gardener” Thomas Pope, who patented in 1807 his “Flying Pendent Lever Bridge,” a rainbow-like “grand parabolic arc,” which is described in detail in the last 50 pages of his 288-page A Treatise on Bridge Architecture published in New York in 1811. That same year he came to Philadelphia and exhibited a model of half of such a bridge which was, by his account, some 50 feet long and weighed 10 tons (1811: 23).
During this time, Pope proposed to build several bridges, but only that for the Lancaster-Schuylkill or Upper Ferry, the future location of a bridge by Wernwag, has survived. Presumably using a plan like his “Flying Pendent Lever Bridge,” he proposed a single span of 432 feet, 46 feet above the water, and estimated to cost $50,000 exclusive of the abutments and covering. That the city fathers ignored the proposal suggests sane leadership on their part. In a footnote in his book, Pope also noted that the specifications printed there were for a single span of 1,800 feet with a “versed sine” (arch rise) of 223 feet over the East River in New York. However mad his idea seems, Pope must be credited with being the most flamboyant bridge designer in American bridge history.
Not far behind was noted portrait painter Charles Willson Peale, who in his 1797 An Essay on Building Wooden Bridges proposed to span the Schuylkill at Market Street with a 390-foot laminated arch bridge rising 39 feet at the center. This rise, however, would have created an horrendous burden on the teams pulling the loads over this unwieldy structure. Pope and Peale wished to attempt such feats because building piers in the deep river was then impossible.
Peale’s drawings for a giant laminated wooden arch bridge show he planned to leave it uncovered. Peale was aware of the option of covering the structure, because he mentioned that bridges with covering already existed. Writes Peale: “It has been advised to make roofs to cover Bridges, and some are so constructed in America; but I conceive this to be a very unnecessary expence [sic], for if the Bridge is not wholy [sic] kept from the wet by such covering, then instead of being a benefit, the roof becomes a disadvantage, by hindering the sun and air from drying and carrying off the moisture; and moreover such high and large surfaces for the wind to act upon, would require a great addition of width in such Bridges. Yet I must acknowledge if ever such coverings are necessary, it must be in the old construction of wooden Bridges with numerous mortices [sic], which are so many deep receptacles for holding water; and it is here that they have their points of bearing, for the support of such arches are only at certain distances, and hence for the maintaining of such constructions, they are obliged to be composed of an immense weight of timber” (1797: 13–14).
Taking Peale at his word, then two things are clear: first, that wooden truss bridges with siding and roofing were in existence at least by 1797 (and probably some years earlier since he wrote this in 1797), and second, that their covering was of no significance other than as a utility. Our current obsession with covered bridges might have struck Peale as odd because he was concerned only with bridges—bridges necessarily built of wood and necessarily protected, either with pitch or weatherboarding. It goes without saying that the covering now thought to be so nostalgic and romantic had no such meanings in early America.
Peale’s observation also suggests that the type of bridge then being covered had some sort of truss because the covering protected the mortise and tenon joinery. Timbers had to be joined because they had to bear stresses both from their own weight as well as from live loads. Therefore, the main reason to cover a wooden bridge was to protect its stress-bearing trusses pinned together with mortises. Since transportation priorities probably dictated that the first bridges would span the most obstructive waterways, therefore these must have been substantial.
