On July 9, 1546, troops under the command of Augsburg's military captain Sebastian Schertlin marched into the Allgäu city of Füssen. A few days earlier, war had erupted between the Holy Roman Emperor and the Schmalkaldic League. Exposed to invasion from the south and the north, Augsburg sat in a precarious position. It was for protection against just such a crisis that the city's magistrates had pursued their program of religio-political expansion. As the war began, therefore, the council encouraged Kaufbeuren to close ranks militarily with Augsburg, while it informed Donauwörth it would “immediately send a detachment of troops…to protect the bridgehead and your city from the enemy.” As part of this strategy to secure the northern and southern passages to the city, Augsburg's magistrates ordered Schertlin to occupy Füssen. A territorial city under the authority of the bishop of Augsburg, Füssen's location at the foot of the Alps made it a crucial gateway to Habsburg Austria. It served as a frequent marshaling station for imperial armies, but on July 9, Schertlin entered the city unopposed. With him came evangelical reform.

Augsburg's council assigned one of its preachers, Holy Cross's pastor Johann Flinner, to accompany Schertlin's forces into the field. Once Schertlin had secured Füssen, Flinner “removed the idols from the churches” and began to preach the principles of Augsburg's reformation. He started by explaining “from Mark that the Gospel does no one harm. I then expounded the end of the second chapter of the Acts of the Apostles.