Here is its story as I told it in 2012 :
President Roosevelt used to shake up preconceptions, often with common sense. In December 1904 he wrote to the Secretary of the Treasury that the U.S. coinage is an "atrocious hideousness"
and suggested to entrust Augustus Saint-Gaudens to redesign the gold coins.
The original of the typed letter, signed by the President, recently discovered, was sold by Heritage for $ 94K including premium in the same sale as the double eagle discussed here.
Inspired by ancient coins, Saint-Gaudens suggests a ultra high relief and begins working on the double eagle ($ 20). Three groups of tests are carried out in 1907. As a whole, no more than twenty coins are minted. Afterwards, the relief will be leveled to facilitate mass production.
One of them, which I described as the most beautiful coin of the United States, in an amazing condition (graded PR69 by PCGS), has been sold for $ 2.76M including premium by Stack's Bowers on June 29, 2012 .
The coin of the next sale has a slight evidence of having been carried in an unidentified pocket and is only graded PR58, but it is exceptional for another reason: it is a coin of the first group, which was extremely limited.
Indeed, only three specimens are identified as originating from this experimental session, from 7 to 14 February 1907. One of them, plain-edged, had one of its dies broken during the minting.
The coin for sale is one of the other two, recognizable by a sans serif typography (something like Helvetica) of the letters on the edge, from a design used at this location on the previous year which will be soon abandoned.