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.
Gateway Arch -- Jefferson National Expansion Memorial. 630 Feet. The Gateway Arch is one of the newest monuments in the National Park system, and at 630 feet, it is certainly the tallest! The Arch is 75 feet taller than the Washington Monument and over twice as tall as the Statue of Liberty. The 60-foot heads carved on the face of Mount Rushmore are designed to the scale of men who would stand 465 feet tall, a height that would easily allow such giants to walk through the legs of the Arch!