As pope he was involved in a dispute over imperial power; he sided against the dukes of Spoleto, whose power seemed a threat to the papacy, but was forced to crown Guido, duke of Spoleto, and his son Lambert.
Encouraged Arnulf to invade Italy, and in 896 Formosus crowned him emperor.
After Formosus’ death, the Spoletos came to power; Formosus' pontificate declared invalid.
PopeJohn XI re-validated his acts, and 897Theodore II re-interred Formosus' body with full honors.