In March of 1902, a continuous line of cut stone more than three-quarters of a mile long closed across the Susquehanna River a few miles north of Harrisburg, Pennsylvania. It was the longest stone bridge the world had ever seen, and it had been raised in about two years. More than a century later, it still stands, and heavy trains still cross it every day. The men who built it called it the bridge built to last forever, and so far, the boast has held.
The river itself was the reason for all that followed. The Susquehanna is broad, shallow, and ancient. Where it passes Harrisburg, it spreads out the better part of a mile from bank to bank. To a railroad, such a river is a wall.
You cannot go around it or through it. You must go over it, and the place you cross becomes one of the most important points on the entire line. The Pennsylvania Railroad had fixed its crossing at a bend called Rockville back in the 1840s, and by the turn of the century, nearly all of the line’s east-west traffic funneled across the water at this single point. The Pennsylvania Railroad was not merely a railroad among railroads.
It called itself the standard railroad of the world, and for once the boast was earned. It was the richest and busiest railroad on Earth, moving more freight, passengers, and money in a year than the treasuries of many nations. At its head stood Alexander Cassatt, an engineer by training who had become president as the 19th century gave way to the 20th. Cassatt believed the only way to hold the lead was to build boldly for a future far larger than the present.
He set out to widen the main line clear across Pennsylvania to four tracks, and in his boldest stroke, he began tunneling beneath the Hudson River to carry his railroad directly into Manhattan, into a great new terminal that would become the original Pennsylvania Station. Every part of that vision rested on the main line behind it being able to carry the traffic. A four-track railroad reaching east from Pittsburgh and the coal fields was worth nothing if it choked down to a bottleneck at the Susquehanna. And a bottleneck is exactly what Rockville had become.
The crossing there was already the third attempt in a single lifetime to bridge the river at that spot. The first bridge, a wooden truss opened in 1849, had been outgrown and gone long before its time ran out. The second, an iron double-track truss built in 1877, had doubled the crossing’s capacity, but within twenty years it too had been overwhelmed, straining under trains far heavier than its builders had imagined. The crossing that fed the busiest railroad on Earth could carry only two tracks.
Here the railroad made a decision that set this bridge apart from nearly every other great crossing of its age. The obvious, modern, and cheap choice was to build once more in iron and steel. Steel was the material of the hour, and a steel bridge could be flung across the river faster and for far less money than a bridge of stone. But Cassatt’s engineers looked past the cost of the first year and thought about the next hundred.
Iron and steel rust; they grow tired and brittle under the endless pounding of the trains, and in the end, however well made, must be pulled down and built again. The railroad had already replaced this crossing twice and had no wish to replace it a fourth time. So they chose stone. A stone arch, built properly, does not hang or pull or strain against rivets and tension.
It stands in pure compression, every stone pressing down and outward against its neighbors, carrying its load the way the ground itself carries the weight of a hill. The Romans grasped this two thousand years ago, and Roman arches still stand. A properly built stone arch does not rust and does not tire. It needs no paint and little repair.
For the busiest railroad on Earth, a bridge that would never need replacing was worth almost any price. The design off the drawing boards was severe and magnificent in its plainness: 48 arches, each a clean half-circle spanning 70 feet, set on massive stone piers standing in the river, with heavy abutments anchoring each end into the shore. The bridge stretched 3,820 feet from end to end and was laid out to carry four tracks, a deck broad enough for the whole flood of the main line to cross abreast. It was never meant to be delicate.
It was meant to look and to be permanent, as solid and unhurried as the hills it joined. The railroad did not hand the whole job to a single contractor. It split the bridge in two down the middle of the river and set two firms building toward each other from opposite banks. The eastern half went to Drake and Stratton; the western half, reaching out from the Marysville side, went to H.
S. Kerbaugh. Overseeing it all, walking the staging day after day and checking the line and levels of every stone, was the assistant engineer George Nauman. The two firms put more than 800 men to work along the banks, including about 300 skilled stone masons, the beating heart of the enterprise.
A common laborer can carry stone, but only a trained mason can cut a rough block of granite to the exact wedge the arch demands and set it dead true. Many of those masons were Italian immigrants, newly landed, carrying a craft older than any railroad. Their knowledge was the same knowledge in its bones that had raised the cathedrals and aqueducts of Europe for a thousand years. Before a stone could be set, the material had to be brought to the river and made ready.
Granite and sandstone were delivered and stockpiled in yards along both banks. In the end, 220,000 tons of stone were handled, shaped, and set in the span of about two years. Building the piers meant walling off sections of the riverbed, pumping the water out, and digging down through mud and gravel until the men struck ground firm enough to carry a mountain of masonry for a hundred years without settling an inch. The river did not stand politely still.
It rises with heavy rains, and in winter it carries ice down its whole length in grinding sheets. Every pier was founded to stand against the current, the floods, and the slow shoving weight of the ice, not for one season but for every season to follow. This was not a bridge built entirely by hand. It could not have been.
No crew of masons, however skilled, could have raised 220,000 tons of stone across the better part of a mile of river in two years by the strength of their arms alone. The Rockville Bridge was built at the dawn of the machine age, and it used the machines of that age without apology. Steam cranes and steam derricks stood along the rising piers, doing the brute lifting, swinging blocks of stone that weighed tons up out of the yards and holding them steady where the masons waited. About 150,000 cubic yards of concrete went into the bridge, filling the deep hearts of the piers and the cores behind the arches.
But the face of the bridge, the part that meets the weather and carries the thrust of each arch, was the patient work of human hands. Behind the smoke of the derricks, the 300 masons cut and set the facing stone in the ancient way, block by block and arch by arch. To turn an arch of stone, the men first raised great curved frames of heavy timber, called the centering, spanning from the top of one pier to the top of the next. Over that wooden form, the masons laid up their dressed stones, beginning low on either side and working upward course by careful course toward the crown.
Until the arch was closed, it could not hold itself up at all. Then came the moment every stonemason both lives for and quietly dreads, when the last stone at the crown, the keystone, was driven down into its place. Only then could the arch stand alone. The centering was eased and struck away, and for one held breath, the arch stood on its own for the first time.
If the work was true, it held. And the work was true. Forty-eight times the men turned the arch, set the keystone, and struck the centering, and 48 times the stone stood. From both banks at once, the two halves crept toward each other across the water, and when they met in the middle, the longest stone bridge in history was closed from shore to shore.
The machine and the hand were not enemies on this river. They were partners, and their partnership is written into every one of the 48 arches. Take away the machines, and the lifting of 220,000 tons of stone would have dragged the work out for a decade or longer. Take away the masons, and there would have been no true arch at all.
Put the two together, set 800 men to it on both banks at once, and the greatest stone bridge in history could rise from an empty riverbed to a finished span in about two years. When it was finished in March of 1902, what stood over the Susquehanna was something the eye could scarcely take in all at once: 48 arches marching away and shrinking with distance until the far end near Marysville seemed almost to touch the horizon. It looked less like a machine than like something that had grown up out of the riverbed. And it went straight to work.
From the day it opened, it carried the full weight of the standard railroad of the world across the river on four broad tracks, swallowing whole the traffic that had choked the old iron bridge. The bottleneck of two generations was broken, and it was broken in stone. Then came the hardest test any bridge can face, not one great storm on one terrible night, but the long, grinding weight of history pressing down year upon year. The bridge carried the traffic of the First World War, the lean years of the Great Depression, and the far heavier burden of the Second World War, when everything a great country could produce rolled toward the coast.
Through all of it, the bridge simply held. And all the while, the trains kept growing heavier, far heavier than the first builders ever had in mind. An iron truss would have been stressed and fatigued and at last condemned by loads like those. But the stone arch only pressed harder down into its own compression.
The harder it pressed, the more solidly it stood. A well-built arch does not resent a heavy load. In its own strange way, it welcomes the weight. Where a steel bridge must be endlessly repainted and forever inspected and sooner or later rebuilt at enormous cost, the great arch at Rockville has asked for almost nothing across the whole span of its life.
The Pennsylvania Railroad that built it is gone now. It grew old, merged with a great rival, and passed quietly into history. The bridge has outlived its own maker. It is not a ruin and not a museum piece.
It is a working railroad bridge today, carrying the long heavy freight trains of the Norfolk Southern Railway across the wide Susquehanna on those same 48 stone arches, and the passenger trains of Amtrak’s Pennsylvanian as well. The men who built it spent about one million dollars on their crossing in stone, a great fortune in the money of that day and far more than a bridge of common iron would have cost. For that one-time cost, paid once and never again, they bought a river crossing that has carried the heaviest traffic on earth for more than 120 years without ever demanding to be rebuilt. The steel bridges of its own generation have nearly all been condemned and torn down and replaced.
The extra price of stone has been repaid a hundredfold in every decade the bridge has stood and worked. It is recognized now as a historic civil engineering landmark, but it wears that honor lightly, because it has never stopped working long enough to settle into being a mere relic. You can still go and stand on the riverbank a few miles north of Harrisburg and look out at 3,820 feet of stone arches reaching away across the wide water toward Marysville, exactly as George Nauman once looked out at the empty river before a single stone of it existed. Wait a little while and a train will come.
You will hear it first, a low sound gathering somewhere down the line, and then the long string of cars will roll out over the river on a bridge built in the first years of the 20th century, carrying the freight of a whole new century its builders never lived to see. And the arches will not so much as tremble beneath it. They built it to last forever, and every train that still crosses it today says plainly that they may yet be proven right.
