On the 29th of March, 1806, President Thomas Jefferson signed a short act of Congress that quietly reshaped the future of the United States. It authorized the building of a road—not just any road, but the very first road the federal government of the young republic would ever build with its own money. It would run west from Cumberland, Maryland, straight over the Allegheny Mountains and out toward the frontier. When finally finished, it would stretch more than 600 miles from the settled East to the deep interior of the country.

Nearly every foot of it, over the mountains and across three states, would be built by men breaking stone with hammers, one piece at a time. This is the story of the first highway in America—the road they called the National Road—and of why you can still drive long stretches of it past the very mileposts its builders set to this day. To understand why a road could matter so much that a president and a congress would break new constitutional ground to build it, you have to understand the shape of the country in 1806. The United States was a nation split in two by a mountain range.

Along the Atlantic coast lay the old settled states, with their cities, farms, and ports. But beyond the Appalachian Mountains, out in the Ohio Valley and the lands of Kentucky and the Northwest Territory, a new America was being born, filling up fast with settlers pouring over the mountains to take up the rich western land. Between those two Americas stood the mountains: a barrier hundreds of miles wide, crossed only by rough traces and Indian trails where a loaded wagon could barely pass, if it could pass at all. This was not merely inconvenient.

It was dangerous to the survival of the country. A farmer in the Ohio Valley, cut off from the markets of the East by an impassable mountain wall, found it easier to float his goods down the rivers to the Mississippi and out through New Orleans—which in those years was foreign territory—than to haul them East to his own countrymen. Thoughtful men feared, with real reason, that if the East and the West could not be bound together by good roads and easy trade, the West would drift away entirely, look South and West instead of East, and the young Union might simply break apart along the line of the mountains. The National Road was, at its heart, an attempt to hold the country together—to reach a hand across the Appalachians and pull the West into the Union for good.

But building it meant crossing a line the country had never crossed before. The Constitution said nothing plainly about the federal government building roads inside the states, and many powerful men believed it had no such right at all—that roads were the business of the states alone. Jefferson himself had deep doubts about whether it was constitutional, and yet the need was so great that he signed the act anyway. A young congressman from Kentucky named Henry Clay took up the cause and made the building of roads and canals—what they called internal improvements—the center of his whole political life.

The National Road was the first great test of the idea that the national government could and should build the physical bones of the nation. Every interstate highway you have ever driven traces its lineage back to that argument and to that first road over the mountains. There was a clever bargain hidden inside the law, too. As the federal government sold off the public lands of the new state of Ohio to settlers pouring West, it set aside a small share of the money from those sales—a fund of two cents on every dollar—and dedicated it to building this road.

So the road to the West was paid for in part by the very westward settlement it was meant to serve. The sale of the frontier funded the road to the frontier. It was exactly the kind of quiet, practical arrangement that let a young and cautious republic do a bold and unprecedented thing without quite having to admit to itself how bold it truly was. The route ran from Cumberland, Maryland, which sat at the head of navigation on the Potomac River—the farthest point west boats could easily reach—and struck out over the Alleghenies toward the Ohio River.

The first great goal was Wheeling, in what was then Virginia, on the banks of the Ohio. The surveyors and builders fought their way over the mountains and reached it in 1818. Choosing exactly where the road would run was itself a great matter, fought over with a ferocity anyone who has watched a modern highway fight would recognize at once. Every town along the mountains wanted the road to pass through it, because everyone understood that the road meant life: a town on the National Road would grow rich on the traffic, and a town left off it would wither and die.

The surveyors were lobbied, pressured, and courted at every turn. In the end, the line they chose largely followed the lay of the land—the way water and game and generations of earlier travelers had already found it, over the passes and along the ridges where a crossing was even possible at all. From there, over the following decades, the road pushed on westward across Ohio and Indiana, aiming for the Mississippi until the money and the will ran out at the town of Vandalia, Illinois, in 1841. More than 600 miles of road thrown across the young country, from the mountains of Maryland to the prairies of Illinois.

Now we come to how they actually built it. A road like this in that age was not poured or paved by any machine. It was built by a method relatively new then, called macadam, named for the Scottish engineer John McAdam. The genius of McAdam was that a road could be made strong and dry not with great slabs of stone, but with layers of small broken stone carefully sized, packed down, and crowned in the middle so that water would run off to the sides instead of soaking in and turning the road to mud.

It sounds simple. The catch is in those two words: broken stone. Because in 1811 there was no machine on earth to break stone. Every stone in that roadbed, over 600 miles of it, was broken by hand.

Men called stone breakers sat by the line of the road with hammers and broke rock piece by piece, endless piece. And they could not simply break it any old way. The stone for the lower layers had to be broken down to a certain size, and the stone for the top surface had to be small enough to pass through a ring only three inches across. So a man would break a rock and test the pieces through his ring and break them again and again until each one was small enough, and then reach for the next rock and begin over.

Think of that labor. Think of the thousands of men it took, sitting along the roadside from the mountains of Maryland to the plains of Illinois, breaking stone with a hammer through their ring hour after hour, day after day, year after year, until they had broken enough stone by hand to pave a road across the mountains and half a continent. It was piecework of the most grinding kind. A man was often paid by the amount of stone he broke and laid—so much for so many yards of road—and so he broke stone from first light until dark to feed himself and his family.

And it was not only men. Along many a stretch, the women and children of the laboring families sat at the stone piles, too, swinging small hammers, sizing the rock through the ring. The sound of it must have been something to hear: mile upon mile of steady hammering, thousands of hammers on stone ringing through the mountain air from dawn to dusk. The work was inspected.

Overseers walked the road and checked that the stone had truly been broken down to size, that no tired or lazy crew had buried great unbroken rocks down in the roadbed to spare themselves the labor. Because a road built of stone too large would rut and heave and break apart within a single season. So the men broke it small, and they broke it right, and the road they made held. The stone was laid in layers—the largest pieces on the bottom, up to seven inches or so, then smaller and smaller stone above, with gravel and soil worked into the top, the whole thing shaped into a gentle curve higher in the middle than at the edges, so the rain would shed off and the road would stay hard and dry.

Over the rivers and deep ravines, the builders raised bridges of cut stone, masonry arches meant to last for centuries, and culverts to carry the streams beneath the road. The greatest of those bridges was the Castleman River Bridge, out in the mountains of Western Maryland, built in 1813. Its single stone arch spanned eighty feet, and when it was raised, it was the largest stone arch bridge in all of America. It was so large and its arch so daring for the time that the story goes people doubted it would even stand once the wooden framing was taken out from under it—that it would crack and fall of its own weight.

It did not fall. When the supports came down, the great arch stood, and it is standing yet more than two centuries later, out there in the Maryland mountains, one of the oldest and finest pieces of the whole National Road still on its feet. To build such an arch, the masons first raised a great wooden framework beneath it, called the centering, shaped to the exact curve the arch was to take. Then they laid the heavy cut stones up over it, both sides climbing toward the top until the final stone—the keystone—was driven into place at the very crown.

Until that keystone was set and the whole ring of stone was complete, the arch was held up by nothing but the wooden frame beneath it. The true test of every stone arch ever built came on the day that framing was knocked away—the moment the arch had to learn all at once to stand on its own or fall. For a span as large and as daring as the Castleman, men truly did not know what would happen. The centering came down, the arch settled a little onto itself, found its footing, and stood, throwing the weight of itself and everything that would ever cross it out and down into the stone abutments on the banks, exactly as the builders had calculated.

It has stood on its own now for more than 200 years, and it will very likely stand for 200 more. The builders were clever in smaller ways, too. Where the road had to cross a stream at an awkward angle, they sometimes built what came to be called an S bridge—a stone bridge laid out in the shape of the letter S, curving so that the span itself crossed the water straight on at a right angle, the shortest and strongest way to bridge a stream, and then curving back to meet the line of the road on either side. Travelers found them strange, and stagecoach drivers cursed the sudden twists, but they worked, and a few of those odd, beautiful S bridges still stand along the old route.

All along the finished road, at every mile, the builders set a marker—a milepost, many of them of cast iron—telling the traveler exactly how many miles he was from Cumberland, where the road began. Mile after mile, all the way to Illinois, a stone or iron post standing by the road to tell you how far you had come and how far you had to go. More than eighty of those original mileposts are still standing today along the modern highway, weathered and old, still faithfully counting off the miles from Cumberland as they have for 200 years. On many of them, below the miles to Cumberland, was cast or carved the mileage onto the next towns down the road, so a traveler could stand at a post in the middle of the mountains and read exactly how far he was from a bed and a hot meal in either direction.

When the road was open, it did exactly what its builders had prayed it would do: it opened the floodgates of the West. From the middle 1820s through the middle of the century, the National Road was the great highway of American migration. Huge freight wagons called Conestogas, their canvas tops billowing and their bodies painted bright blue and red, hauled tons of goods west and the produce of the frontier back east, rolling along at perhaps fifteen miles in a day. Faster stagecoaches, carrying passengers and the mail, could cover sixty or seventy miles in a day, racing between the towns.

And in among them trudged the settlers—whole families with everything they owned, walking west toward new land—and the drovers, driving great herds of cattle and hogs and even flocks of turkeys along the road to the eastern markets. In the space of a single generation, an entire new heartland of the country was settled, the states of the old Northwest filling up with farms and towns and growing cities, and a very great share of the people and goods that built them came west along this one road. The cities of the Midwest, the whole broad center of the nation, were in a real sense the children of the National Road. The Conestoga wagon was a marvel in its own right, a machine purpose-built for hauling heavy loads over rough and mountainous roads.

Its bed was curved, higher at each end and dipping in the middle, so a heavy load would settle toward the center and not shift or spill on the steep grades. Its wheels were tall and broad to keep it from sinking into the mud, and it was pulled by teams of four or six great heavy horses. The teamsters who drove them were a rough, proud, fiercely independent breed of men, known up and down the road. They smoked a cheap thin cigar that took its name from the wagons they drove—the stogie—a word we still use for a cheap cigar to this very day.

An entire world grew up along the road to serve that traffic. Taverns and inns sprang up so thickly that it was said there was a tavern for nearly every mile of the road. The finer stagecoach taverns served well-to-do travelers with good beds and good food, while humbler wagon stands took in the teamsters and drovers and their animals for the night. Long before there was any way to keep meat cold, the only way to bring it to the Eastern cities was to walk it there alive, and so the National Road was, for a good part of every year, a slow-moving farmyard.

Great herds of cattle and droves of hogs were driven east along it, mile after weary mile, and even flocks of turkeys and geese were walked all the way to market, their feet sometimes coated in tar and sand to protect them over the long hard road. It was loud, and it was dirty, and it was gloriously, unmistakably alive. The road also stayed near the very center of the nation’s politics, because the great argument over whether the federal government had any business building such things never truly ended. President Andrew Jackson, only a few years later, would famously veto a bill to fund another such road, believing it a step too far for the power of Washington.

With that veto, the whole grand vision of a national web of federal roads and canals stalled for a generation. And so the National Road stood for a long time as very nearly the only one of its kind—a single lonely proof of what the country could build when it chose to act together, in an age that could never quite decide whether it ought to act together at all. For a few decades, the National Road was the beating heart of the young country’s inland trade, and it did the great thing it was built to do. It bound the West to the East.

It made it easy, for the first time, to move the wheat, whiskey, and livestock of the Ohio Valley to the markets of the coast, and to carry the coffee, sugar, and manufactured goods of the East out to the frontier settlements. It knit the two halves of the country together across the mountains that had threatened to divide them. It helped to make sure that the American West would grow up looking east toward the Union and not away from it. A road built by men breaking stone with hammers had helped to hold a nation together.

And then a new thing came along and swept the old one aside. The new thing was the railroad. Beginning in the 1850s, the Baltimore and Ohio and the Pennsylvania Railroad drove their iron lines west over and through the same mountains. A train could carry more, faster, cheaper, and in any weather than any wagon or coach on any road.

The traffic drained off the National Road and onto the rails almost overnight. The great Conestogas disappeared. The taverns emptied and closed. The tollgates came down.

By the time of the Civil War and after, the first highway in America had fallen quiet, its stone breaking up under the weather, its mileposts leaning, its once-crowded taverns falling into ruin. But it did not die, and its second life came from an invention its builders could never have dreamed of: the automobile. In the early 1900s, as Americans took to the roads in their new machines, they rediscovered the old National Road and began to fix it up and use it again. It was folded into a route called the National Old Trails Road, and then in 1926, when the country laid out its first system of numbered federal highways, the old National Road became a large part of United States Route 40, one of the great East-West highways of the automobile age.

The road that had carried Conestoga wagons now carried Model T Fords. For many of the towns along it, the National Road simply became—and remains to this day—their Main Street, which is why it earned the affectionate old name: the Main Street of America. Along the old road in the 1920s, a patriotic women’s society raised a series of tall stone statues of a pioneer mother—a woman striding westward with a baby in her arms and a small child clinging to her skirts—called the Madonna of the Trail, set up in state after state along the route to honor the countless women who had walked that road into the West with everything they owned on their backs. What the railroad had taken away, the automobile, in a strange and fitting twist, quietly gave back.

The National Road is still there, under your wheels. Drive United States Route 40 across Maryland and Pennsylvania and Ohio and beyond, and for mile after mile you are driving on the very line the surveyors laid and the stone breakers paved two centuries ago. You will pass the old stone mileposts still counting the miles to Cumberland. You can pull over and walk across the Castleman River Bridge, that daring eighty-foot arch that men swore would fall and never did.

You can find the strange old S bridges standing in the fields. You can eat in taverns that fed the drovers and stagecoach travelers of the 1830s. There are stretches where you can leave the modern highway entirely and walk the old original roadbed itself—a quiet lane in the woods—and see the crown of it still shaped as the builders shaped it, and the old stone bridges still carrying it over the streams. There are tollhouses preserved as little museums, their windows angled so the keeper could see traffic coming from both directions at once.

The past is not sealed away here behind glass; it is out in the open, along 600 miles of it, for anyone at all who is willing to slow down and look.