Bp. of Mainz from 1850 and a pioneer in modern Catholic social thought. Preaching at the episcopal conference at Fulda in 1869, he drew attention to the contradictions between economic liberalism and Christian principles. At the First Vatican Council (1869–70) he opposed the definition of Papal infallibility on the ground that its promulgation was ‘inopportune’. He also opposed the Kulturkampf, championing the freedom of the RC Church in Germany from State control.