When I was growing up, the Mall was my playground. Once, in the late '30s or early '40s, a guard took us to a manhole cover not far from the Washington Monument, removed it and showed us a small "monument" inside. He said it was there to check how the monument settled. My wife thought I was making it up until I checked with my brother and found that he vividly remembers it, too. Is it still there?

Bob Garber, Lusby

Yes, it is -- just one of the secrets buried in Washington. The concrete mini-monument is about 15 feet tall, tapering from three feet at its base to 1.5 feet at its top. In the 19th century, not long after the Washington Monument was completed, its midget counterpart was placed 50 feet south of it, encased in a circular brick wall.

So, what the heck is it?

It's what engineers call a "benchmark," which our dictionary defines as "a mark of known or assumed elevation from which other elevations may be established."

The idea was that the mini-monument, because it weighed a lot less than its 81,000-ton big brother, wouldn't sink into the ground. Thus, any change detected in the big monument in relation to the lil' monument would be the result of earth settling underneath the mega-memorial. (The bases of both are at the same level. The reason the small one is now underground is that tons of dirt were carted in to build up the grounds surrounding the 555-foot obelisk.)

If you think this is a rather crude arrangement, you're right. For starters, how can you be sure the peewee pillar isn't sinking itself? Because of that, the diminutive shaft isn't used anymore for its original purpose. But it's still there, an oddity under a metal manhole cover, like something from a pharaoh's tomb.

John F. Kelly

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A guard points to the mini-monument entombed near its towering counterpart.