America's Covered Bridges. Ronald G. Knapp

deck above supported by heavy wooden corbels running at 45 degrees from the vertical posts to the deck beams and forming what appears as a simple triangular “arch.” Considering the limited construction technology of the day, it is a wonder that mere men could place such heavy timbers within a dangerous river bed and complete such a long-lasting structure (Litwin, 1964: 13).

      A possible “missing link” in American bridge history is the “Leffingwell Bridge,” named after the nearest landowner. According to Frances Manwaring Caulkins, writing originally in 1845, and quoting a newspaper article from June 20, 1764: “Leffingwell’s Bridge over Shetucket river at Norwich Landing [Connecticut] is completed. It is 124 feet in length and 28 feet above the water. Nothing is placed between the abutments, but the bridge is supported by Geometry work above, and calculated to bear a weight of 500 tons [sic]. The work is by Mr. John Bliss, one of the most curious mechanics of the age. The bridge was raised in two days and no one hurt. The former bridge [Edgerton’s bridge] was 28 days in raising” (1874: 348).

      The Connecticut River, running between Vermont and New Hampshire, passes through an especially rugged gorge at Bellow’s Falls, Vermont. In 1785, Colonel Enoch Hale managed to construct a beam bridge supported by angle braces here that lasted until 1840, though no photographs of it are known. (NSPCB Archives, R. S. Allen Collection)

      This scale model, believed to be John Bliss’s 1764 “Geometry Bridge,”also called Leffingwell’s Bridge, over the Shetucket River at Norwich, Connecticut, is kept at the Faith Trumbull Chapter of the Daughters of the American Revolution (DAR) house in Norwich. (Gerald Dyck)

      Caulkins continues: “This bridge retained its position, and the proprietor was allowed a portion of the toll for fourteen years. But in 1777 it was much injured by floods, and the town having purchased Leffingwell’s remaining interest, united with Preston in petitioning the Legislature (May session, 1778) for leave to raise money by lottery for the erection of a new bridge. The petition was granted” (p. 348).

      “Geometry bridge” suggests the use of a truss. Considering that Palladio’s work had been known after its translation into English was published in 1738, it is entirely possible that builders here and there were constructing at least modest spans, almost certainly not covered. Indeed, Caulkins later refers to a bridge standing in 1813 as “the Geometry Bridge at Chelsea” (p. 349).

      The Faith Trumbull Chapter of the Daughters of the American Revolution (DAR) in Norwich possesses a large-scale wooden model of uncertain age that purports to depict the old bridge. If this is accurate, then we can be sure a “geometry bridge” was an open double polygonal arch with posts forming four panels. While polygonal arch covered bridges exist in Germany and Switzerland, they are generally more complex, suggesting that Bliss either knew something of such precedents or independently invented it. Otherwise, the Leffingwell Bridge appears to be an isolated, one-of-a-kind design.

      Between Hale’s brave span of 1785 and Palmer’s fully covered “Permanent Bridge” in 1805, a mere twenty years, American bridge technology made tremendous strides thanks to a small group of incredibly savvy, bold, and self-taught “bridge carpenters.” All of the documented bridges, because they spanned major rivers, required extensive amounts of cut and sawed timber, thousands of tons of massive stone blocks, and hundreds of men, horses, and their necessarily simple tools. Additionally, every project had to be initiated with private capital because the governments of the time were not yet in the business of building roads and bridges. Risking great amounts of money to construct bridges over dangerous and wild rivers that routinely flooded with both water and ice floes each year, these early entrepreneurs appear to have lost out more often than they succeeded. In those days, investing in a bridge company was no sure way to safeguard one’s assets or increase one’s equity, and thus the bridge building business developed slowly.

      Published by Ebenezer Turrell Andrews and Isaiah Thomas in The Massachusetts Magazine in 1793, “Newbury Bridge over Merrimack River” clearly shows Timothy Palmer’s Deer Island Bridge between Salisbury Point and Newbury constructed as open trusses in 1792. The left span was 113 feet long plus open trestle spans, and the right span was 160 feet, both using arch-reinforced trusses. The north span (left) was covered in 1810 and survived until 1882 while the south span (right) was replaced in 1810 by a chain suspension bridge. (Boston Athenaeum)

      At least six major bridges were constructed over Massachusetts’ Merrimack River between 1792 and 1795. Three men were chiefly responsible: Moody Spofford, Jacob Spofford, and Timothy Palmer, all living in nearby towns. Of these, Palmer, of Newburyport, became the most famous, though he is said to have learned his skills from the Spoffords. Together with Jacob Spofford, Palmer first designed and built the Deer Island Bridge between Newbury and Salisbury Point, also known as the Essex Merrimack Bridge, in 1792, only seven years after Hale’s corbel-supported bridge at Bellow’s Falls. The Essex Merrimack Bridge Company was authorized on May 30, 1791, and their charter granted on January 9, 1792. Amazingly, the bridge opened in late November (one source gives November 26, another November 20) of that same year. Two historians, Laura Woodside Watkins and Richard Sanders Allen, have written brief histories of the bridge, Allen’s 1996 study contradicting Watkins’ 1961 one on several points.

      The Essex Bridge crossed the river in two segments separated by Deer Island. According to an engraving and plate description published in The Massachusetts Magazine in May 1793, the bridge’s length was 1,030 feet in total. The northern segment, connecting Salisbury Point to the island, consisted of three short trestle spans, one of them a 40-foot draw, between what were likely piers of wood cribbing, completed with a trussed span of 113 feet to the island. The southern portion was mainly a trussed span of 160 feet. The engraving contradicts the description in several ways, showing the shorter trussed span with ten panels and the longer one with eight, and also not mentioning the long approach on the Newburyport side shown in the engraving. According to the drawings, the multiple kingpost trusses have arched upper and lower chords with either corbels or arches reinforcing the bridge from beneath. If accurate, the engraving suggests that Palmer had followed the basic principles of Palladio’s designs, especially that of his bridge over the Brenta River at Bassano, Italy, “at the foot of the Alps” (1738: 67–8). In December 1792, only a month after the bridge’s opening, The Massachusetts Magazine noted “The arch is deemed the largest on the continent. The whole work contains more than 6000 tons of timber. Mr. Timothy Palmer, an ingenious house wright of Newburyport, has received a medal, for the best construction of an arch.” By 1810 the southern span had deteriorated to the point that it was torn down and replaced by a novel chain suspension bridge based on the patent design of Judge James Finley of Pennsylvania and built by John Templeman of Georgetown, Maryland (now District of Columbia), and Palmer’s close associate, Samuel Carr. The north span, covered around 1810, survived until 1882. A photograph in the R. S. Allen archives shows this remaining span as a fully covered double-lane structure with one or more arches beneath the trusses and deck.

      A view from the shore of Palmer’s Newbury Bridge long after being covered, showing part of the trestle and drawbridge approach. (NSPCB Archives, R. S. Allen Collection)

      In 1793, two major bridges were built, but the first of them, the Middlesex-Merrimack Bridge at Lowell, Massachusetts, also called the Pawtucket Bridge, consisted of three open flat-deck spans, the eastern two braced with corbels and the longer western span supported by an arch placed beneath the deck. The designer and builder may have been Col. Loammi Baldwin (1745–1807). Reports say that it was “rebuilt” in 1795 and again in 1805.

      The second was the Andover Bridge over the Merrimack built by Timothy Palmer and Moody Spofford, reportedly for 3,998 pounds, but there are no known illustrations. It was described as having three spans with wooden piers, the center span being 110 feet. Considering who built it and the length, we would assume it to have been another arched truss bridge.