Nearly everyone knows about the Tomb of the Unknowns. When I was growing up it was called the Tomb of the Unknown Soldier, even though there were (at that time) two people buried there. At one point there were four buried there, but they managed to identify the soldier from Vietnam, so right now they're just three.

I think I was first introduced to this monument some time in early grade school, perhaps as early as 1976, when the country was going bananas over the bicentennial and you couldn't even see through all the red-white-and-blue bunting. Even though I was only 8, it was easy to take to heart the somber, serious attitude of the thing. You knew immediately just by looking at it that it was important.

The problem I had was that nobody could really explain to me why it was so important. We had better technology than they did back then, why not climb in there and figure out who they are? My parents seemed puzzled that I would even ask the question, but they really couldn't come up with a good answer either. I eventually stumbled upon my own explanation, that every family that had someone go MIA could believe that it was their son inside that tomb. But even then I knew that, while important, that probably wasn't the whole story.

This lack of a good explanation struck me hard a second time several years ago when my wife's mother and sister came up to visit. We took them to Arlington and they got to watch the changing of the guard and a laying of a wreath at the Tomb of the Unknowns, probably two of the most moving moments in a very moving place.

But again, I was asked not only by Nina, Ellen's sister, but also by Suzanne, Ellen's mother, why? Why is this here? What does it mean? It's not that they denied its importance, they just didn't understand. Again, I didn't have a good answer. I mumbled something about a nation's promise to its soldiers that even if we can't find you we'll remember you and while I knew this was again part of it, I also knew it wasn't quite right.

A few months later I read The First World War by John Keegan, and finally I had my answer.

You see, the US isn't the only country with a monument to unknown soldiers. Every major combatant in World War One has them. England, France, the Netherlands, Germany, and most others have somber memorials that contain unidentified remains.

And that is the key. At heart, these memorials are World War One memorials. Over time other things have been added, even other soldiers, but the aspect of the First World War is always the most prominent. I think that this is, again, a case of "forgetting how to build a pyramid". Everyone knew why they were built, when they were built, and so nobody really bothered to write it down. The things are so somber and so important you always feel embarrassed to ask what the original point of it is, and so it ends up being forgotten.

World War One was the first war of the mechanized age. It was the first war where horrifically large numbers of men were literally blown to bits. Previously, after a big battle, you could go out and collect all the bodies, identify most if not all of them, and if nothing else at least bury them all in a place that could be visited later on. You couldn't do that in World War One.

Millions of men were thrown up over the tops of trenches and tens of thousands of them simply ceased to be. The First World War was the war for artillery, like nothing really before or since, and the effects of a direct hit from a 155 mm howitzer shell (hint: it's as big around as your head) on a human body don't really take much imagination.

And this didn't just happen to a few dozen poor bastards who happened to be in the wrong place at the wrong time when charging a cannon emplacement. One of the utter horrors of that war was that this happened again, and again, and again, and again for years at a time. You sometimes knew Joe got it in the last battle because you yourself saw his head blown open like a watermelon hit with a hammer. But sometimes Joe just didn't come back, and no matter how hard you looked or where you looked or when you looked you knew you'd never find him, because all that was left were some teeth and a few bits of bone scattered across the hundred foot radius of a random shell impact.

And these fragments were everywhere. What were you supposed to do after a battle when you found a jawbone under your foot, still glistening with its meniscus layer intact? Or when you looked up and saw thousands... millions of these fragments glistening in the morning sun the day after a charge?

So while the Tomb of the Unknowns has become many things to many people, all of them valid and important and deeply felt, originally the Tomb of the Unknown Soldier was erected in memory to all those men that didn't just give up their lives but gave up their very identities in a terrible, terrible war. The remains of the soldier inside the tomb are a symbolic reference to the tens of thousands of soldiers who will never, can never be buried. We don't identify those remains because they're a symbol of all the ones that won't, can't, ever be identified. We guard those remains because we want to express that such a sacrifice is supreme beyond all others, and therefore requires the most supreme honors we can bestow.

And that, to me at least, is what the Tomb of the Unknowns means.