Historians consider the papal bull Unam sanctam - which proclaimed that there is no salvation outside of the Church - to be one of the most extreme statements of papal spiritual supremacy ever made.

It stemmed from Pope Boniface VIII's ongoing feud with Philip the Fair of France over Philip's taxation of clerics without papal consent.

Unam sanctam thus emphasized that Catholic princes are subject to the pope in temporal and religious matters.

Pope Boniface VIII Issues Unam Sanctam in 1302. How did Philip respond to the bull?