How we remember speaks to who we are: "It may seem obvious to say that memorials are for the living, not for the dead. But it bears repeating, a reminder of all the purposes behind our urge to memorialize."

"We often say, as we do so prominently at the United States Holocaust Memorial Museum in Washington, that we must never forget. But sometimes we build memorials to do just that. A kind of debt paid, as historian David Glassberg puts it, so that we can move on.

"We seek immortality through memorials, but not necessarily for those whom you might think. The Greek temple from which Abraham Lincoln presides over the National Mall is a statement by the generation that produced it—that they themselves did not forget. The World War II Memorial just opened at the other end of Lincoln's Reflecting Pool does the same.

"'It almost becomes like an obligation that had to be fulfilled,' says Glassberg, author of 'Sense of History: The Place of the Past in American Life.' 'There is the feeling that somehow or another, if we didn't, we would be shamed.'"

"News coverage has propagated the notion that the World War II Memorial is late. In fact, it's right on schedule. Agitation to commemorate wars tends to come about 50 years after they end. Lincoln's temple wasn't dedicated until 1922, or 57 years after he was assassinated.

"The best memorials, in fact, require time. 'There needs to be time passed to let people debate what the meaning was,' says Kenneth Foote, author of 'Shadowed Ground: America's Landscapes of Violence and Tragedy,' a study that raised questions about why some sites were memorialized and others were not. Foote found it was not unusual for debate to last a generation or more.

"The Vietnam Veterans Memorial, appearing in 1982, was an aberration, an attempt to ameliorate the lingering pain of that unpopular war — to separate, as the National Park Service says, 'the sacrifices of the veterans from the U.S. policy in the war.' That's why it's a 'veterans' and not a 'war' memorial."

"Washington, D.C., is a city of memorials — especially war memorials. Civil War figures from the victorious Union forces dominate public spaces. They are familiar sights, but do they carry forward the message of their age?

"'Not far from the White House, Admiral Farragut stepped onto a pedestal in 1881, but he is all that's left of that time in the square that still bears his name,' Thomas Mallon noted in a 2001 essay for the Save America's Treasures project. David Farragut's famous exhortation to 'Damn the torpedoes!' survives from the Union victory at Mobile Bay. But how many passersby connect the man on the pedestal to those words?

"The Austrian critic Robert Musil said in 1936 that there is something about memorials that repels our attention—meaning, Glassberg explains, that these things are left over from a previous time, and are almost immediately obsolete.

"Glassberg disagrees. 'I think a memorial remains meaningful if it's reinterpreted by each generation,' he says. Martin Luther King Jr. did that with his 'I Have a Dream' speech at the Lincoln Memorial.

"Arguments over meaning, in Glassberg's view, are what keep memory alive—more so than the monuments we build. 'That,' he says, 'is probably a more valuable piece of work for society to do.'"