4 For these reasons We have ever repeatedly encouraged the recitation of theHoly Rosary, and have endeavoured to increase its dignity by a more solemn cult,following in this the footsteps of our predecessors. Pope Sixtus V., of happymemory, approved the ancient custom of reciting the Rosary; Gregory XIII.dedicated a day under this title, which Clement VIII. afterwards inscribed inthe martyrology, and Clement XI. extended to the Universal Church. BenedictXIII. inserted the feast in the Roman Breviary, and We, ourselves, in perpetualtestimony of Our affection for this devotion commanded that the solemnity withits office should be celebrated in the Universal Church as a double of thesecond class, consecrating to this devotion the entire month of October. Finallywe ordered the addition to the Litany of Loreto of the invocation "Queen ofthe most Holy Rosary," as an augury of victory in our present warfare.
Source: Diuturni Temporis (Vatican.va)