The settlers who built the bridge spanning Pennypack Creek's shallow, rippling courses shaped the stones in its three neat arches with hand tools and raised its nearly 20-foot spandrels with just the strength in their own bodies.
They were likely people from Sweden and England, living near the edge of a colonial frontier, and they took the stone from the land near the creek. The bridge was built just wide enough — about 20 feet — to accommodate horse-drawn carriages traveling the King's Highway to and from Philadelphia.
Over the last 320 years, the road named to honor a monarch became Frankford Avenue. Forest around the bridge gave way to apartment buildings and pizza shops, and carriages evolved into cars and SEPTA buses. But the bridge still stands, the oldest active stone bridge in the United States, according to PennDot.
The 73-foot-long bridge has aged, though. One of its stone walls is cracked and buckling, a consequence of water seeping through the road surface and damaging the stone beneath. The nearly 15,000 vehicles that cross it every day have taken their toll, too, in crashes that have damaged stone.
PennDot has listed the Frankford Avenue Bridge — which has also been called the Pennypack Creek Bridge, Holmesburg Bridge, and King's Highway Bridge — as "structurally deficient," and this month is beginning a rehabilitation project intended to extend the Holmesburg span's life without sacrificing its historic value.
"It's irreplaceable," said Din Abazi, an assistant engineer with PennDot. "They took great care."
A bridge is deemed structurally deficient if it received a rating of "poor" or worse on its road deck or underlying structures.
The $3.2 million project is part of a larger $7.2 million program to rehabilitate seven "structurally deficient" bridges in Philadelphia, Montgomery, and Delaware Counties, which itself is part of Pennsylvania's ongoing effort to improve a staggering number of bridges statewide in need of work. The state, which once had more than 6,000 structurally deficient bridges, has cut that number nearly in half as of this January.
The Frankford Avenue Bridge, which is listed on the National Register of Historic Places, requires special attention. The restoration had to be vetted and approved by the federal Department of the Interior to ensure the bridge's historic value is preserved.
Historians say George Washington, John Adams, and Ulysses S. Grant all would have used the bridge.
It was erected during a period of rapid growth in the United States, when the boundaries of what belonged to which colony were under dispute, said local historian Fred Moore, of the Friends of Northeast Philadelphia History Network.
In 1681, just 16 years before the bridge was likely built, about 500 white settlers, most of them Swedes, lived in Pennsylvania, according to a U.S. Census report. The numbers of Native Americans in the area, including the Lenape Indians, had been decimated by illness and didn't number many more than the settlers, Moore said.
Just four years later, the population ballooned to 7,200, after William Penn's settlers arrived. Almost three times as many people were living in the area just five years after that, according to U.S. Census Department research.
The border between Pennsylvania and Maryland was disputed at the end of the 17th century, Moore said, and Penn, whom the historian described as something like a modern-day land developer, was eager to attract more people to the land to bolster his claim. The area around the bridge itself was largely unsettled, Moore said, without even an inn nearby. But easy crossings over the waterways between Philadelphia and New York City would have been an attractive incentive for people to make homes in the region.
At the time the bridge was built, Pennsylvania law required all men of a community participate in the construction — or pay taxes — but Moore thinks this span was built as part of a business' initiative that included a grist mill erected about a quarter-mile downstream. The bridge's original construction included a narrow culvert, still there, that channeled water to the mill's paddles.
The exact date of the bridge's completion is unclear, though evidence points to the mill and the bridge being installed in 1697. Modern engineers estimated it would have taken two to five years to finish the structure, which used arches to support the surface in a simple design that dates to the Roman Empire. To this day, parts of the bridge look identical to the way they did at the birth of the 18th century, when its builders could have stood along the creek's banks to admire their finished work.
"That is so important about the bridge and really any old structure like that," Moore said. "You can go and touch it and say this is 300 years old."
The modern rehabilitation will take considerably less time — about six months, PennDot estimates.
The bridge has undergone previous repairs. During a major reconstruction in 1893, workers raised the surface several feet and more than doubled its width to make space for trolley tracks. The widening installed new masonry on the bridge's eastern side. Much of the work to be done in 2018 will focus on the western side, some of which is original.
This week, workers prepared to channel all the creek's water through one of the arches, leaving the two others dry and easier to work on. Eventually the water will be diverted again to repair the final arch. The project will tear up the bridge's deck, sidewalk and railing. Workers will replace much of the earth infill beneath the pavement with a light concrete that will be less permeable to water, said Mike Cuddy, an expert on stone bridges and senior vice president with TranSystems Corp., a Kansas City, Mo.-based transportation contractor.
New sidewalks and guard rails will be added. Part of what holds the bridge together is the weight pressing down on the stones, and the structure will have to be buttressed to ensure that stones don't fall out of place as the surface is removed.
The other major stage of construction involves disassembling much of the stone spandrel down to the arches. Those will be repaired as needed, the leaks stopped, and the wall rebuilt using the original stones as much as possible. The reconstruction will require a special mortar, as modern materials are too strong and would over time tear apart the stone.
Though engineers didn't want to estimate how long the bridge would be usable without the repairs, they did say winter cold could contribute to conditions in which the leaks would cause a stone wall to crumble at any time.
"It's very vulnerable, I would say," Abazi said, "and it's hard to judge the life span."
The project will lift the current 20-ton weight restriction on the bridge and should add at least 50 years to its usable life span.
Six of the 10 oldest stone bridges in the country are in Pennsylvania, but none nearly so old as the Frankford Avenue Bridge.
The bridge's longevity is due in part to other roads taking the place of the main thoroughfare that the King's Highway once was, but also to the ingenuity of the people who built it more than 300 years ago.