On January 27, 1816, with the brief from Pope Pius VII, the Austrian territories were separated from the Diocese of Chur and subsequently assigned to the two dioceses of Brixen and Trento, marking the end of a thousand-year history of the oldest diocese located north of the Alps, which had maintained its historical boundaries unchanged since the 8th century. Following the acquisition in 1819 of the former territory of the Swiss Quarter of the now-defunct Diocese of Constance, a new era began for the ecclesiastical district of Chur, which has been documented since 451 and was likely founded from Milan in the late 4th or early 5th century. The purpose of this first richly illustrated volume is to make its history accessible to a broader readership, focusing on the period of the Christianization of Raetia and its founding.