1 Mariengroschen - John Frederick

John Frederick, Duke of Brunswick-Lüneburg-Calenberg, converted to Catholicism in 1651 — a remarkable anomaly in a Protestant territory — yet managed to retain his duchy and govern until 1679 without triggering the confessional crisis his conversion might have caused elsewhere. The Mariengroschen denomination itself was a fixture of Lower Saxon small change, its name derived from the Virgin Mary imagery conventional to the type, and it circulated heavily enough that survivors in collectible condition are genuinely scarce.