At the Cass Gilbert symposium held this morning at the Mattatuck Museum, a mystery was raised by the presenters. The front of the U.S. Supreme Court building, under the pediment, is engraved with the phrase "Equal Justice Under Law".
The Associate Curator of the U.S. Supreme Court, Matthew D. Hofstedt, informed us that the origin of the phrase is currently unknown. A quick Google search turns up a Wikipedia page dedicated to theories about the origin of the phrase, but (not too surprising) Wikipedia doesn't have the answer. The Wikipedia page has been recently updated to make reference to the stencil over the entrance to the Veteran's Memorial chamber in the Waterbury City Hall. The stencil leads one to believe that the phrase was created by Cass Gilbert.
As pointed out by the experts in attendance today (Barbara Christen and Robert Gryzwacz), we don't have any documentation to prove that the stencil dates from 1915--it could have been added later.
I can't resist a challenge like this. No one knows? Really? Ooooo! Let me do some research!
What I discovered is not at all surprising. Cass Gilbert, who added quotes from Abraham Lincoln to several places in the Waterbury City Hall building, got this phrase from Lincoln.
I found a reference to it in an 1883 publication by The Chautauqua Institute, which pretty clearly attributes it to Lincoln. Unfortunately, they don't cite their source, so I don't know which speech or letter it comes from. And a search on the Library of Congress database of Lincoln's papers doesn't turn it up. But I'll keep digging!
UPDATE 4/12/2011: The word is that the inscription in City Hall is not original, that it was added during the 2010 renovation. Additionally, (as pointed out to me by Matthew Hofstedt) even though the title page of the above-mentioned Chautauqua Institute book on Google Books is for an 1883 publication, the portion containing the phrase is from a speech written in 1936.