Map showing the limits of the Prince-Bishopric and the Diocese of Augsburg. In the Holy Roman Empire, the secular principality of a bishop, his prince-bishopric, was always smaller than his diocese, where his authority was limited to spiritual and church matters. In the course of the Reformation, many of the states covered by the diocese of Augsburg became protestant. Therefore the traditional boundary of the diocese, as shown on this map, no longer reflected reality on the ground. Dillingen became the residenz (capital) of the prince-bishop once Augsburg, a free imperial city, became fully independent of its former ecclesiastical master.