The Half-Union was a gold United States coin minted as a pattern in 1877 with a face value of US$50, and weighed roughly 2.5 ounces. It was never struck for circulation, due to the belief that it would only circulate among banks.
A Full Union, with the face value of 100 dollars, was never made due to the failure of the Half-Union.
In 1915, a commemorative Panama-Pacific International Exposition Half-Union was issued in two forms: round and octagonal. It had a gladiator-like figure on the front and a wisdom owl on the back. Both coins were designed by Robert Aitken, and all Panama-Pacific Half-Unions were minted in San Francisco.
Today, the commemorative 1915 round and octagonal $50 coins sell for multiple tens of thousands of dollars in any condition.
With a mintage of just 483 the round $50 coin has, in fact, the lowest mintage figure of any official U.S. mint issue of the 20th Century.
At the 1915 Exposition, these coins were sold both individually and in framed sets. Not surprisingly, few were purchased, as few could afford $50, let alone a small premium on the coins.