The church of the Immaculate Conception in Piacenza, consecrated in 1681, was built together with the adjoining convent at the behest of Ranuccio II Farnese, as a thanksgiving for the healing of his third wife Maria d’Este. Nothing has survived of the sumptuous pictorial and sculptural decoration of its interior, due to carelessness. An unpublished manuscript, entitled Succinta Spiegatione, allows an accurate reconstruction. The author of the work is the Jesuit Domenico Gamberti, already at the service of the Este family as an iconologist, and – in this facility – extender of a complex iconographic program focused on the theme of the Immaculate Conception. The description of the decoration, which consists of biblical heroines, prophets and conceptual emblems, is used as the occasion for an apology of the Marian mystery and is part of the heated and centuries-old theological battles on the dogma of Conception. The authorship of the architectural project – so far assigned to Domenico Valimages, but attributable to the famous Gian Giacomo Monti – has also been clarified. This contribution gives account of the ephemeral apparatuses made under ducal orders for the solemn ceremony through which the Benedictine nuns made their entrance into the monastery. With the new “Tempio Verginale,” a new processional path was opened, giving the city not only a clear testimony of the magnificence of the founders, but also one of the most magnificent, and so far unknown, glorifications of the Conception mystery in the Po area.