The Peace of Augsburg, signed in 1555, was a treaty that allowed for the coexistence of Catholicism and Lutheranism within the Holy Roman Empire. This agreement marked a significant turning point in the religious conflicts of the Reformation, as it established the principle of 'cuius regio, eius religio,' meaning that the ruler of each territory could determine its official religion. The treaty aimed to bring stability to a region torn by religious wars and set a precedent for later religious toleration.