I Guess Most Of Us,

will recognise this famous landmark,

 the Washington Monument, built to honour George Washington, the commander-in-chief of the Continental Army and the first President of the United States, once the tallest building in the world, at just over 555 feet, but how many know there is a second much smaller obelisk near to the one we all know and see?

 unknown to most passersby, there’s a 12-foot-tall replica of the Washington Monument under a manhole near the actual monument, officially known as “Bench Mark A,” this underground oddity is actually a Geodetic Control Point that’s used by surveyors, it is part of the network of a million control points across the country that helps the National Geodetic Survey, or NGS, synchronise all of the government’s maps,

 according to NGS modernisation manager Dru Smith, “Geodetic control points provide starting points for any map or measurement, it has to be more accurate than any measurement you do on top of it, so we pick things that tend to be extremely stable, all the surveys we’ve done, going back to the early 1900s, have used it,” says Smith, most recently, it was used in the aftermath of the 2011 Washington earthquake, measurements over the past century have shown that the Washington Monument has sunk 6.2 centimetres into the marshy soil below, at an average rate of 0.5 millimetres per year, the mini-monument was placed in the 1880s as a part of a trans-continental levelling program, the mini-monument was above ground for a time, before being encased in a brick chimney and buried, outside of surveying circles, it’s been largely forgotten, the survey marker is underneath a manhole, just south of the Washington Monument, now this is very important, Speak to a Park Ranger before trying to see it.