Complex sentence: Although the belief was widely held since at least Late Antiquity, the doctrine was not formalized until December 8,1854 by Pope Pius IX in his Papal bull "Ineffabilis Deus", and it is not formal doctrine except in the Roman Catholic Church.
Split into simpler sentences: Although the belief was widely held since at least Late Antiquity, the doctrine was not formally proclaimed until December 8,1854, by Pope Pius IX in his papal bull "Ineffabilis Deus". It is not formal doctrine except in the Roman Catholic Church.