Page "Immaculate Conception" Paragraph 16

During the reign of Pope Gregory XVI the bishops in various countries began to press for a definition as dogma of the teaching of Mary's immaculate conception.

Pius IX, at the beginning of his pontificate, and again after 1851, appointed commissions to investigate the whole subject, and he was advised that the doctrine was one which could be defined and that the time for a definition was opportune.

On 8 December 1854, in a great assembly of bishops in St Peter's Basilica at Rome, he promulgated the Bull Ineffabilis Deus, in which the history of the doctrine is summarily traced, and which contains the definition as given above