One of the most important examples of the spectacular 1907 ultra-high relief Saint-Gaudens $20 has sold with superb results at Heritage Auctions' January 7-12 FUN US Coins Signature Auction in Orlando.

The coin was altered soon after its initial issue, with the design proving impractical yet undeniably beautiful

The coin is unique and was once part of the estate of engraver Augustus Saint-Gaudens. The design is considered one of the most beautiful, yet impractical, ever seen in US numismatics.

Engraved with the initials "ASG" on the edge and graded PR68 by both NGC and PCGS, the coin sold for $2.1m.

The coin came into existence due to President Theodore Roosevelt's desire to see new currency during his presidency, which would showcase America's status as a world leader in both industry and the arts. He recruited Saint-Gaudens, a well know sculptor and engraver, who had previously worked on a series of monuments for Washington DC's parks.

With Roosevelt describing the US' existing coins as "artistically of atrocious hideousness", Saint-Gaudens produced the elaborate design at his request, but it was soon found to be impractical, requiring 11 strikes to bring up the detail in the mint.

Additionally, the coins could not be stacked with other denominations, and the high-relief design was soon changed. Congress also intervened to add the words "In God We Trust" after some complained the words were not included, as they had been with all other coins.

There are several variations of the coins, issued between 1907 and 1933, but it is the ultra-high relief coins that are the most desirable to collectors.

The coin is one of two struck for the mint cabinet, but it was later awarded to Saint-Gaudens' widow. Saint-Gaudens never got to see the design in circulation, having died in August 1907.

Selling as top lot in the sale was a 1792 US Birch cent, which made $2.5m, while a 1793 Chain cent achieved $2.3m.