In Suprema Petri Apostoli Sede

The letter "In Suprema Petri Apostoli Sede" was issued by Pope Pius IX in 1848. It addressed the Catholic Church's stance on mixed marriages and the education of children from such unions, asserting that children should be raised in the Catholic faith.1

Pope Pius IX had one of the longest pontificates in Roman Catholic history, serving from 1846 to 1878. During his papacy, he convened the First Vatican Council, where papal infallibility was defined as dogma in 1870. The Petrine theory, which forms the basis of the papacy, asserts that the Apostle Peter was the first pope and his ministry was passed down to his successors, the bishops of Rome. This theory is rooted in biblical passages where Jesus grants Peter a unique role and authority.1234