A Roman gold aureus with a unique heifer design on its reverse is expected to attract big bids at Dix Noonan Webb's Ancient and World Coins auction on September 22 in London.
The coin, well-known to collectors as a piece of numismatic genius, is estimated at ?�300,000-350,000 ($508,000-593,000).
It was struck circa 27-18 BC, and depicts Emperor Augustus, founder of Rome, on its obverse.
The heifer design on the reverse is based on a lost masterpiece of Greek sculpture, and just 22 examples are known with this feature. Fifteen of those are housed in museums, leaving just seven available to private collectors.
The coins known to numismatists are divided into five types, dictated by variations in the portrait of Augustus (some feature a bald head, others a laureate head) and also the direction both Augustus and the heifer are facing.
This is the unique Type 2 coin with the laureate head of Augustus facing right and the heifer facing left. It remains in remarkable condition, described as "extremely fine with lustre".
"This is a truly extraordinary coin," says Christopher Webb, head of the coins department at Dix Noonan Webb.
"Not only is it a unique type of an already very rare coin but its condition after more than 2,000 years is extremely fine and visually it is a beautiful work of art. It also represents an epic period when Augustus built an empire that changed the course of human history."
Paul Fraser Collectibles offers a range of exceptional rare coins for sale - see our store today.