Denier - Sergius II and emperor Lothair I

This joint issue reflects one of the more unusual arrangements in early medieval monetary history: a sitting pope and a Carolingian emperor sharing authority on the same coin. The collaboration stemmed from Lothair I's Italian coronation and his formal recognition of papal temporal authority under the Constitutio Romana of 824, which bound successive popes to seek imperial confirmation before consecration. Sergius II was the first pope actually consecrated without that confirmation — then compelled to send his brother to Lothair's court to smooth over the breach.