The last time such destruction was seen on these shores, it happened in places like the Maryland West-Virginia border, set amid serene farms and rolling hills where Americans fought each other and died.

The battle of Antietam in Maryland nearly devastated the two armies that fought it and forever changed the community that was its accidental host. And photography, then an emerging medium, dramatically increased its impact on the country, in a way not altogether different from today's images of American lives lost to terrorism.

The wars in Europe that claimed so many in the 20th century were thousands of miles away; the conflicts in Korea and Vietnam even further. The attacks on the World Trade Center and the Pentagon have been compared to Pearl Harbor, but in 1941, that was an outpost on a distant island -- a small colonial territory, not a state -- its bombing leaving America feeling more victimized than vulnerable.

Once, though, armies marched through this very land, bent on destroying each other with the explosive fury of those fuel-laden hijacked airplanes.

"One of my rangers came up to me on Tuesday," said David Howard, superintendent of Antietam National Battlefield. "He said we had always called this battle the bloodiest day in the history of this country. But that might not be true anymore."

Four thousand people were killed here -- another 19,000 left wounded or missing -- in the one-day battle that occurred Sept. 17, 1862. That's twice as many American deaths as on D-Day. No one can say for certain if it is more than died on Sept. 11, 2001.

There are 4,776 Union dead buried in Antietam National Cemetery -- from this and other battles fought in Maryland -- 1,836 of them unknown. Another 200 veterans of subsequent wars were buried here before the cemetery was closed in 1953. It was reopened this year to accept the body of Patrick Howard Roy, a 19-year-old sailor from nearby Keedysville, Md., who died in the terrorist attack on the USS Cole.

Many of the dead of Antietam lay on the battlefield for days, their corpses captured by the cameras of Alexander Gardner and James E. Gibson, assistants of Mathew Brady. A few weeks later, Brady opened an exhibition in his studio at 10th Street and Broadway in New York, not far from what would be the site of the World Trade Center. No one had ever seen anything like "The Dead of Antietam." These pictures were seared into the minds of those who saw them as deeply as the image of the jetliner slicing into the World Trade Center is now etched into ours.

"Prior to this, the war was rendered in romantic paintings that depicted men in spotless uniforms," said Ted Alexander, senior historian at Antietam battlefield. "Now the Brady studio displays photographs of bloated corpses, some in its storefront so people walking down Broadway could see them.

"It was the first media wake-up call," he said. "It made people realize this was serious business."

A mural-size photograph from that exhibition of dead laid out in front of Dunker Church confronts those who enter the visitors center at Antietam. Howard says that many pause before it, almost all noting the pair of shoes that sit eloquently in one corner.

For many in the North particularly, the Civil War had been a distant fight, and unless the casualty lists contained the name of a husband, brother, son or friend, it remained an abstraction. The photographs changed that, just as the pictures of the icons of New York and Washington falling to the terrorist assault on Tuesday, Sept. 11, changed our view of our vulnerability.

Ken Burns, who produced the acclaimed documentary The Civil War a decade ago, says that among his first thoughts when he saw the destruction of the World Trade Center were words Abraham Lincoln said in 1838.

Burns can recite them: "Shall we accept some trans-Atlantic military giant to step the ocean and crush us at a blow? Never! All the armies of Europe, Asia and Africa combined, with all the treasure of the Earth ... could not by force take a drink from the Ohio or make a track on the Blue Ridge."

"I committed that to memory 12 years ago," Burns said over the phone from New Hampshire. "I've used it to explain our special protections, bordered by two oceans with friendly neighbors to the north and south. But that's no more. In some ways we have to re-set and everything begins anew."

Lincoln's point was that if we were to be destroyed, it would come from within. And that has always been the origin of such destructive forces -- whether in armies of the Civil War, the bullets of John Wilkes Booth and Lee Harvey Oswald or the bomb of Timothy J. McVeigh, ours have been internal affairs, family squabbles that we can take care of ourselves.

In large measure -- as any who have lived overseas can testify -- this is because we are relatively free of the ethnic conflicts that constantly threaten other countries and that are at the root of last week's terrorism.

Even in the Civil War, Irish Catholics fought side-by-side with German Lutherans and English Anglicans -- on both sides of the conflict -- a unity that was inconceivable in Europe for generations. In many places, it still is.

It is no accident that our largest war was fought over an ethnic issue -- the fundamental racial flaw built into our constitution -- or that the most serious civil disturbances in the years since have echoed that conflict.

"If you have ever traveled in Europe, you see submachine-toting guards everywhere, and you know how lucky we are," Burns says. "We are the only country born of an idea. We are not here because of geography or religion or race or even economics. We are here because everybody agrees on an idea. It's that idea that is imperishable."

But suddenly those oceans that had for so long protected that idea --

and that kept our cities gleaming, our factories churning, while Europe was destroyed -- seem no larger than the English Channel did in World War II.

Certainly, the United States was invaded in 1812, the White House burned by British troops. But that invasion was repulsed. The English eventually joined the French as our friends and -- a century later -- it was our decision to travel across that protective ocean to help them.

So it was in places like Sharpsburg, the town that adjoins Antietam battlefield, that the unsettling uncertainty so many felt last week was last felt in this country.

"This was kind of like living on the Arab-Israeli border," said Alexander of the environs of Antietam. "There was constant troop activity. From the spring of 1861 until the end of the war, tens of thousands of troops of both sides moved through here."

Alexander said Sharpsburg "was the first established community in the history of the republic to suffer such intense abuse."

It was a different sort of war than is fought today. There were no blitzkriegs or V2s or carpet bombings or atomic weapons or terrorist acts. Civilian casualties were relatively few -- two occurred at Gettysburg. None has ever been confirmed at Antietam. Officers from both sides knocked on farmhouse doors to inform the occupants that the battle was coming their way. But death was everywhere, and the future was unknown.

There were no twin towers to collapse, but according to Alexander, practically every house in this town of 1,300 was hit by an artillery shell. With more than 100,000 troops in the area, with 23,000 dead and wounded, with livestock killed, crops destroyed and disease rampant, the people of Sharpsburg would never be the same after the battle.

Few more evocative pieces of land exist in this country than the small depression near the center of the battlefield that was called Sunken Road. It became known as Bloody Lane after the corpses of Confederate soldiers lay so deep that Union soldiers said you could walk across the bodies.

Especially in the silence that the absence of airplanes in the Dulles flight path brought this past week, it is possible to evoke the horror that this strip of land contained -- a terror that must have equaled whatever went on in those hijacked airplanes, whatever lies below the wreckage of those buildings.

Though nothing like Gettysburg, Antietam has its share of monuments to those who fought and died. Where will the monuments to the heroes of this new war be placed? Where United Flight 93 went down, not in a national landmark but in a desolate patch of Pennsylvania after passengers fought their hijackers for control? In the midst of the bustling financial district where firefighters headed into the huge damaged buildings all others were trying to escape?

On the post-Civil War tombstones in Antietam National Cemetery, there is the name of the conflicts that the deceased fought -- Spanish-American, World War I, World War II, Korea. But not on the tombstone of Patrick Howard Roy. His war still has no name.

Hill is a Baltimore Sun reporter.