According to the Papal Bull Commissi Nobis Divinitus, dated 6 December 1708, Pope Clement XI mandated the feast as a Holy Day of oligation which is to be celebrated in future years by the faithful.Commissi Nobis Divinitus - VI Decembris 1708 - Clementis XI, Papam - Sincera itaque nostra erga eamdem augustissimam caeli reginam, patronam, advocatam, nostram, devotione incitati festum conceptionis ipsius beatae mariae virginis immaculatae ubique terrarum in posterum ab omnibus et singulis utriusque sexus christifidelibus sicut alia festa de praecepto observationis festorum comprehendi auctoritate apostolica, tenore praesentium decernimus praecipimus et mandamus. ...Volumus autem ut earumdem praesentium literrarum transumptis, seu exemplis etiam impressis, manu alicuius notarii publici subscriptis, et sigillo personae in ecclesiastica dignitate constitutae munitis, eadem prorsus fides adhibeatur ipsis praesentibus si forent exhibitae vel ostensae. Furthermore, the pontiff requested that the papal bull be notarized in the Holy See to be further copied and reproduced for dissemination.
