He wielded little temporal power, ruling during the struggle between John Crescentius and Emperor Henry II for the control of Rome.
During his whole pontificate, he was allegedly subordinate to the head of the Crescentii, who controlled Rome, the patricius (an aristocratic military leader) John Crescentius III.
Rome was wracked with bouts of plague, and Saracens operated freely out of the Emirate of Sicily ravaging the Tyrrhenian coasts.
He authorized a new Diocese of Bamberg to serve as a base for missionary activity among the Slavs, a concern of Henry II.
[7] John XVIII abdicated in July 1009 and, according to one catalogue of popes, retired to a monastery, where he died shortly afterwards.