The story of the “Cadaver Synod” is kind of like the ninth-century version of the McDonald’s hot coffee lawsuit: On the surface it sounds silly, but once you learn the facts, it actually makes sense.
In the ninth century, the pope had the power to crown the Holy Roman Emperor. This meant that popes were involved with political intrigue, and many of them didn’t live long after assuming office. Stephen VI’s predecessor, Formosus, reluctantly crowned the Duke of Spoleto as the Holy Roman Emperor and later crowned the duke’s son, Lambert. In 896, Formosus reversed course and crowned one of his allies, King Arnulf of the East Franks. Shortly after becoming emperor, Arnulf became paralyzed and returned to his native Germany, and Formosus himself perished.
When Stephen VI took the papacy, the crowning was still in dispute. Stephen had closer ties to Lambert and wanted to reinstate his ally, and the Cadaver Synod was a means to deligitimize Formosus and all of his decisions as pope.
Stephen ordered Formosus’s nine-month-old corpse be clothed and actually brought to the courtroom, and he appointed a deacon to speak on the departed’s behalf. During the sham trial, Stephen accused the cadaver of everything from perjury to violating canonical law.
What was left of Formosus was found guilty and thrown into the Tiber River. But the trial itself was so controversial that Stephen’s reign only lasted a few more months, until he was stripped of his papal seal and executed.