In last week’s column we discussed some very old bridges in the Bridgeville area and in Allegheny County. The positive feedback we received from that column has encouraged us to follow up on our promise to do another column on this subject.
Part of our difficulty evaluating old bridges is the extent of replacement some of them have experienced. This bring to mind the old story of George Washington’s Axe. It has been reported that visitors to Mount Vernon are provided the opportunity to split a piece of firewood using the very axe that the “father of our country” used to chop down the famous cherry tree.
When the docent is asked to confirm that this is indeed the axe he used two hundred and eighty years ago, the reply is “Absolutely! And we have only had to replace the handle sixteen times and the head nine”. Similarly, our judgments on the provenance of an old bridge is frequently arbitrary.
If we expand our area of interest to all of Southwestern Pennsylvania, we can add several dozen covered bridges and the oldest iron bridge in the country, the Dunlap’s Creek Bridge in Brownsville. Designed and constructed by Captain Richard Delafield, U. S. Army Corps of Engineers, it was completed in 1839 and is still in service today.
The bridge spans eighty feet and is supported on five shallow arches, each constructed of oval shaped thin-walled cast iron tubular segments, bolted together. The segments are very similar to sections of steam boilers. In its earliest days this bridge was a key component of the National Road, the primary artery for western migration in the nineteenth century.
Also a part of the National Road is the even older “S” bridge, near Claysville. Originally completed in 1818, it was a two-span stone arch bridge over Buffalo Creek. The “S” designation recognizes that its approaches, parallel to each other, are at an angle to the main span. This was a common practice in the early nineteenth century whenever a road did not approach a stream at right angles. The “S” bridge has been bypassed, but is still in existence.,
Extending our circle enough to spill over into neighboring states allows us to add the Wheeling Suspension Bridge, built in 1849, and the Casselman Bridge, built in 1813. Like Dunlap’s Creek and Claysville, these two bridges were important elements of the national Road.
When Charles Ellet’s Wheeling Bridge was completed, it was the longest suspension bridge in the world. Ellett won the contract to build it after severe competition from John Roebling. In 1854 its deck was destroyed by high winds. Description of the torsional deformation of the deck is eerily similar to that of the Tacoma Narrows Bridge (a.k.a. “Galloping Gertie”) eighty-six years later.
The Wheeling Bridge spanned the main channel of the Ohio River from Wheeling to Wheeling Island. It was supplemented by a small bridge from the Island to the Ohio shore, over the back channel of the river.
Located near Grantsville, Maryland, the Casselman Bridge is a magnificent stone arch structure, spanning eighty feet over the “Little Crossings” of the Casselman River. When it was built, it was the longest single span bridge in the United States. David Shriver Jr. is credited with its construction. Still in good condition, it has been bypassed by a relocation of U.S. Route 40, the descendant of the National Road.
We need extend our circle only to the eastern part of Pennsylvania to include the oldest surviving roadway bridge in the United States, the Frankford Avenue Bridge in Philadelphia. Built in 1697 to connect William Penn’s mansion with the city, it immediately became a key link of the King’s Highway, which connected Philadelphia with the cities to the north.
The Frankford Avenue Bridge has three stone arches, two of them spanning twenty-five feet, which carry the roadway over Pennypack Creek. In 1893 it was widened to permit trolley traffic. Even that addition easily qualifies as “centenarian”! Still in use today, it carries a load rating of twenty tons.
What about world-wide? The website “oldest.org” gives that distinction to the Arkadiko Bridge in Argolis, Greece. Dating back to about 1200 B.C. and credited to Mycenaean Greeks, it looks like a pile of rocks piled across a ravine with an arch-shaped opening to let storm-water pass under it.
Second oldest are the Tarr Steps in Somerset, England. Constructed about 1000 B.C. by “the Devil so he could sunbathe”, they consist of a series of large rocks serving as piers, supporting thick rock horizontal deck slabs.
Next comes the “Caravan Bridge” over the River Meles near Izmir, Turkey. It is a nearly semi-circular stone arch spanning about fifty feet. Prominently mentioned in Homer’s writings, it is believed to date back to 850 B.C. It looks more like something someone actually planned and built; it is my candidate for the oldest true bridge.
The number still in existence that are more than eighteen centuries old is impressive. It also includes the Karamagara Bridge in Cappadocia, Turkey (550 B.C.) and the Limyra Bridge in Lycia, Turkey (300 B.C.). Then come numerous handsome bridges built by the Romans – Pons Fabricius in Rome, Italy (62 B.C.); Ponte di Tiberio in Rimini, Italy (20 A.D.); Pon du Gard in Languedoc, France (50 (A.D.); the Alcantara Bridge in Alcantara, Spain (106 A.D.); Ponte Sant’Angelo in Rome, Italy (134 A.D.); and the Cendere Bridge in Adiyaman Province, Turkey (200 A.D.).
History and bridges are two of my favorite interests; combining them to produce these two columns has given me a lot of enjoyment. We engineers are proud of the ability we have today to design and build effective bridges; I am not certain our accomplishments can begin to compare with those of the unsophisticated builders whose products have survived for centuries.