The Universal Postal Union, founded in Bern in 1874, established the principle that member nations would treat international mail as a single unified postal territory — a genuinely radical idea that standardized rates and transit rules across sovereign borders for the first time. Greece joined in 1875, one year after the UPU's founding congress. The €6 face value places this squarely in the Bank of Greece's ongoing commemorative program, which has used that unconventional denomination since the early 2000s specifically to sidestep bullion coin classification under EU regulations.
The Universal Postal Union, founded in Bern in 1874, established the principle that member nations would treat international mail as a single unified postal territory — a genuinely radical idea that standardized rates and transit rules across sovereign borders for the first time. Greece joined in 1875, one year after the UPU's founding congress. The €6 face value places this squarely in the Bank of Greece's ongoing commemorative program, which has used that unconventional denomination since the early 2000s specifically to sidestep bullion coin classification under EU regulations.