The five Panama–Pacific commemorative coins were produced in connection with the 1915 Panama–Pacific International Exposition in San Francisco. Struck at that city's mint, the issue included round and octagonal $50 pieces. Excepting modern bullion coins, these two gold pieces are the highest denomination ever issued and the largest coins ever struck by the United States Mint. The octagonal $50 piece is the only U.S. coin to be issued that is not round.