Final answer:
The papacy reached its pinnacle of power in the early thirteenth century under Pope Innocent III, who expanded papal influence over secular rulers.
Step-by-step explanation:
The power of the papacy peaked during the early thirteenth century under Pope Innocent III. Innocent III's papacy marked a period where the papal authority expanded significantly, showcasing the pinnacle of papal power during the Middle Ages. He skillfully utilized his spiritual authority to strengthen the Church's influence over secular matters, a practice that began with earlier popes like Gregory the Great.
Innocent III's tenure saw the Church assert dominance over European monarchs, even engaging in political affairs by deposing and appointing kings. This commanding role of the papacy in both religious and secular realms reached its height under his rule, before later challenges like the Avignon Papacy and the Great Western Schism would emerge and shake the papacy's powerful standing.