1 Ducat - Frederick William I

Frederick William I had little patience for luxury — he famously dissolved his father's extravagant court, sold off the silverware, and dressed like a common soldier — yet the Prussian ducat continued to be struck in near-pure gold throughout his reign, primarily to pay foreign mercenaries and settle trade debts where bullion quality was contractually non-negotiable. The ducat circulated internationally by weight and fineness, not by royal decree, which meant a reputation for debased coinage would have cost Prussia far more than the metal itself.