Brigadier General William Tecumseh Sherman (finding his commander on the first night of Shiloh): Well, Grant, we’ve had the devil’s own day, haven’t we? Ulysses S. Grant: Yes. Lick ‘em tomorrow, though.

Our offices are ten blocks up Fifth Avenue from Washington Square Park, whose gateway is a triumphal arch designed in the 1890s by Stanford White, flanked by two statues of George Washington, one as soldier, one as president. It’s an unsatisfactory gateway because it is undergoing what seems to be an eternal restoration and, for years, has been caged by a chainlink fence.

So, I was walking around rather than through the arch one day in early September when I heard a sound that was at once familiar and incomprehensible. I looked to my right, and coming toward me were two police horses, side by side, panicked and galloping, fully caparisoned for duty, tethered nightsticks bouncing against their empty saddles. I jumped a low fence and got behind a tree. The horses clattered past and away across the sunny park as mothers snatched their children to safety.

Well, I thought, that’s the scariest thing I’m likely to see for a while. I watched police catch and subdue the horses while, off to the south, the towers of the World Trade Center glittered serenely in the late-summer sunlight.

A week later, coming through the park on another midday, looking for the thousandth time at the haze of smoke or dust in the empty south, I walked into a small crowd and discovered that the drab fence had been turned into a shrine. Scores of bouquets hung in its grid; hundreds of votive candles burned at its base, pale in the bright sunshine. On the fence, along with the flowers, were messages—not the heartbreaking family portraits posted everywhere begging for information about their subjects, but rather letters of thanks to firefighters, to police officers, to all the dead who had died trying to save people they’d never met. Above these transient messages was a permanent one, carved into the monument, a phrase of George Washington’s: “Let us raise a standard to which the wise and the honest can repair.” During our brief national history, a great many Americans have died trying to help people they never met.

Two days before the flowers came to the fence, I’d stood in a street near our office on the most beautiful morning since the world began: clear, cool, so immaculate that the north tower of the World Trade Center might have been its small, precise simulacrum in the souvenir plastic globes filled with glittering debris that tourists take home with them. But now, there was an oblong hole canted across its whole face, black smoke fuming off the top.

The man next to me explained what I was seeing, and after a while, I replied, “This happened before, in 1945. A bomber flew into the Empire State Building.” I sounded fatuous; what I’d meant to say was