How did Pope Innocent III expand the Papal States?

Pope Innocent III significantly expanded the Papal States by leveraging the power vacuum created by the death of Emperor Henry VI. While his predecessors generally limited their claims to the area immediately surrounding Rome, Innocent pursued a more expansive strategy to establish papal temporal authority.12

His methods included:

• Diplomatic Maneuvering: He exploited the rivalry between the Hohenstaufen candidate, Philip of Swabia, and Otto IV for the imperial throne to promote papal claims, particularly in the march of Ancona. In 1201, Otto formally acknowledged the church’s right to the duchy of Spoleto.12
• Systematic Administration: Innocent dispatched papal legates to cities across central Italy to secure their loyalty. Through these efforts, cities including Ancona, Assisi, Perugia, and Spoleto declared their allegiance to the pope.2
• Military Fortification: To solidify control over Rome itself, he ordered the construction of the Torre dei’Conti, a massive military fortification.2

By the end of his pontificate, Innocent had established a larger territory than any of his predecessors, effectively functioning as a powerful secular prince in central Italy.2