12 Mariengroschen - John Frederick

John Frederick ruled Calenberg from 1665 until his death in 1679, a period during which he converted to Catholicism in 1651 — a striking anomaly in a predominantly Lutheran territory. His conversion created persistent friction with his subjects and the broader Lower Saxon Circle, yet his coinage continued largely uninterrupted, the 12 Mariengroschen being a workhorse denomination of the regional silver currency system tied to the Lüneburg Kreistalers of the period.

The Mariengroschen itself was a north German accounting unit with deep roots in the bishopric of Hildesheim, where the denomination originated in the late medieval period.