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.
Made of some 36,000 blocks of marble and granite stacked 555 feet in the air, the monument was the tallest structure in the world at the time of its completion in December 1884. In the six months following the dedication ceremony, over 10,000 people climbed the nearly 900 steps to the top of the Washington Monument.