Denier - Gregory IV and emperor Lothair I

Gregory IV died in January 840, and the joint coinage with Lothair I places this issue within the turbulent years immediately following the death of Louis the Pious — a period in which the Carolingian empire fractured among warring sons. Gregory had actively intervened in that conflict, crossing the Alps in 833 to mediate, though his efforts achieved little beyond a brief and humiliating capitulation at the so-called "Field of Lies" near Colmar. The papal-imperial joint denier was itself a political instrument, advertising an alliance that was never as stable as the coin implies.