20 Francs - Napoleon III

Napoleon III's gold 20 francs was the workhorse of the Latin Monetary Union, the multinational currency agreement France anchored in 1865 alongside Belgium, Italy, and Switzerland. The standardized specifications were designed explicitly so that member nations' gold coins could circulate interchangeably — a rare instance of 19th-century monetary cooperation that actually functioned as intended for over a decade.

Production at the Paris mint ran at extraordinary volume through the 1860s, fueled by Californian and Australian gold flooding European markets. The Franco-Prussian War of 1870 ended the run abruptly; hoarding began the moment Prussian troops crossed the border, and gold disappeared from circulation almost overnight.