Baring-Gould’s sources: German Martyrology. No trustworthy authorities for his life and acts. The following account is from the Augsburg Breviary.

Dionysius , together with his sister Hilaria, (August 12th), her daughter Afra, (August 7th), and the rest of his family, was converted and baptized by S. Narcissus the bishop, afterwards chief pastor of the Church of Gerona, in Spain, (March 18th.) As Narcissus was obliged to leave the little band of Christians at Augsburg, he instructed, and then ordained, Dionysius to be their priest, or, as some writers assert, their bishop. Thus Dionysius became the spiritual father of a little family of true believers, and was called to encourage them during the fiery trial of persecution. He saw his sister Hilaria, and her daughter Afra, glorify God by martyrdom. Knowing that his own turn had come, he fortified himself with the Holy Sacrament, yielded himself into the hands of those who sought his life, and dying a martyr's death, gained the crown and palm.

The relics [the bodily remains of a saint, or objects they used, kept with honor] of this saint, who is reckoned the first bishop of Augsburg, together with those of Quiriacus, were discovered in the year 1118, and were translated by the abbot Egino to the Church of S. Ulrich, in Augsburg, and enclosed in an altar. Later, in the year 1258, Hartmann, bishop of Augsburg, opened this altar, and placed them, on 26th Feb., in a new altar, dedicated to SS. Dionysius and Quiriacus, and he ordered that this day should be observed as the festival of S. Dionysius. The Church of Augsburg honours him as her first bishop, though the episcopal see of Augsburg [a bishop’s “see” is his diocese, named from his seat (Latin sedes)] was not regularly constituted till 250 years later, when Sosimus became the first of a succession of prelates which from that time to the present has not failed.