Because Ubaid, Sumer, Akkad, Assyria and Babylon civilizations all emerged around the Tigris-Euphrates, the theory that Mesopotamia is the cradle of civilization is widely accepted.
If you Google for washington monument height, the first listing you see is for a page about the monument at greatbuildings.com. Note that the page mentions that the monument has a base of 55 feet and a height of 555 feet, in keeping with what they call the standard Egyptian proportion of 10:1 height to base.
Ben Sherman of the National Geodetic Survey says the latest survey of the monument's height was completed in 1999 and that the current work is part of an ongoing historical survey, which began in 1901. Located on the National Mall, the Washington Monument opened to the public in October 1888.