A Significant Historic Structure
The covered bridge is an important and significant historic structure in the Commonwealth of Pennsylvania. Not only does Pennsylvania have the most extant covered bridges today, it probably had the most during the height of, the covered bridge period 1830 to 1875. Estimates have been made that Pennsylvania once had at least 1500 covered bridges, historically known as "kissing" or "wishing" bridges because young couples used the shaded passages to steal a kiss while others would make a wish before entering a new bridge for the first time. Not only is the sheer number important, but Pennsylvania had the first known U.S. covered bridge, as well as the prototypes for most of the major truss types.
The first US covered bridge was located in Philadelphia over the Schuylkill at 30th Street and built in 1800 by Timothy Palmer, a master carpenter from Newburyport, Massachusetts. The investors asked to have it covered in the hopes of extending the life of the bridge and Palmer reluctantly agreed. The value of the covered design was quickly recognized. The true reason for covering bridges was to extend the life of the bridge by protecting the side supporting timbers (not necessarily the floorboards) from exposure to the weather, thus lowering maintenance costs of the bridge.
From the completion of this first bridge, the age of the covered bridge was upon Pennsylvania. Not only were the truss types of Burr and others first tried out in Pennsylvania, but the covered bridge spread as the local carpenter adapted it to the local problem of crossing the numerous small streams and creeks throughout Pennsylvania. The covered bridge is also important in the history of bridge building. The early stone arch bridges were really only practical on smaller streams and then in areas with an abundance of good building stone. The peak of the stone bridge is Pennsylvania can be seen in the Rockville Bridge over the Susquehanna River built by the Pennsylvania Railroad and contains a quarter of a million tons of stone. The covered bridge was the transition from the stone to the cast-iron in most places.
Since the heyday of the covered bridge they have been rapidly disappearing through neglect, flood, arson and progress. Prior to the Agnes Flood of 1972, Pennsylvania had 271 covered bridges, spread across 41 of its 67 counties. Since that time the number has been decreasing at a fast rate.
The Delaware River and its watershed area of fourteen counties once had the most -- and some of the earliest -- covered bridges in Pennsylvania. At one time the Delaware River itself was crossed by twenty-one interstate covered bridges. All but the railroad bridge at Easton were originally built by companies interested in the tolls that could be collected.
Three top covered bridge architects built across the Delaware River; the 1806 Theodore Burr Bridge between Morrisville and Trenton, second oldest covered bridge in the United States; the 1806 Timothy Palmer Bridge at Easton; and the 1814 Lewis Wernwag Bridge at New Hope. None of the 21 bridges remain.
The northern watershed area of Wayne, Pike, Luzerne, and Monroe Counties had only a handful of covered bridges originally and only one of these, the Bittenbender bridge in Luzerne County, still remains.
In the Lehigh River area the covered bridge was more abundant. Carbon County has only two remaining bridges, one of which was saved only by its removal by the Beetzville Dam project area. Lehigh has retained six of its original wooden spans but Northampton only one.
Bucks County today retains 12 of its original 36 covered bridges, most of them in Upper Bucks. The strict usage of the Town truss within the county is unusual and represents the largest number of Town truss bridges anywhere in the State.
The lower watershed area has seen the greatest disappearance of the covered bridge. Originally six wooden bridges spanned the Wissahickon Creek alone; today only the Thomas Mill bridge remains. In an area that saw the birth and development of the covered bridge, these rare survivors are the only remaining examples of an important stage in the development of bridge technology and history.
Sources of information: Covered Bridges of the Delaware River Watershed -- a National Register of Historic Places thematic resource nomination.