"The Jews had no nine days' religious celebration or nine days' mourning or feast on the ninth day after the death or burial of relatives and friends. They held the number seven more sacred than any other. On the contrary, we find among the ancient Romans an official nine days' religious celebration whose origin is related in Livy (I, xxxi). After a shower of stones on the Alban Mount, an official sacrifice, whether because of a warning from above or of the augurs' advice, was held on nine days to appease the gods and avert evil. From then on the same novena of sacrifices was made whenever the like wonder was announced (cf. Livy, XXI, lxii; XXV, vii; XXVI, xxiii etc.). "Besides this custom, there also existed among the Greeks and Romans that of a nine days' mourning, with a special feast on the ninth day after death or burial. This, however, was rather of a private or family character (cf. Homer, Iliad, XXIV, 664, 784; Virgil, Aeneid, V, 64; Tacitus, Annals, VI, v.). The Romans also celebrated their parentalia novendialia, a yearly novena (13 to 22 Feb.) of commemoration of all the departed members of their families (cf. Mommsen, "Corp. Inscript. Latin.", I, 386 sq.). The celebration ended on the ninth day with a sacrifice and a joyful banquet. There is a reference to these customs in the laws of the Emperor Justinian ("Corp. Jur. Civil. Justinian.", II, Turin, 1757, 696, tit. xix, "De sepulchro violato"), where creditors are forbidden to trouble the heirs of their debtor for nine days after his death. St. Augustine (P.L., XXXIV, 596) warns Christians not to imitate the pagan custom, as there is no example of it in Holy Writ. Later on, the same was done by the Pseudo-Alcuin (P.L., CI, 1278), invoking the authority of St. Augustine, and still more sharply by John Beleth (P.L., CCII, 160) in the twelfth century. Even Durandus in his "Rationale" (Naples, 1478), writing on the Office of the Dead, remarks that "some did not approve this, to avoid the appearance of aping pagan customs".
"Nevertheless, in Christian mortuary celebrations, one finds that of the ninth day with those of the third and seventh. The "Constitutiones Apostolicae" (VIII, xlii; P.G., I, 1147) already speak of it. The custom existed specially in the East, but is found also among the Franks and Anglo-Saxons. Even if it was connected with an earlier practice of the pagans, it nevertheless had in itself no vestige of superstition. A nine days' mourning with daily Mass was a distinction, naturally, which could be shared by none but the higher classes. Princes and the rich ordered such a celebration for themselves in their wills; even in the wills of popes and cardinals such orders are found. Already in the Middle Ages the novena of Masses for popes and cardinals was customary. Later on, the mortuary celebration for cardinals became constantly more simple, until finally it was regulated and fixed by the Constitution "Praecipuum" of Benedict XIV (23 Nov., 1741). For deceased sovereign pontiffs the nine days' mourning was retained, and so came to be called simply the "Pope's Novena" (cf. Mabillon, "Museum Italicum", II, Paris, 1689, 530 sqq., "Ordo Roman. XV"; P.L., LXXVIII, 1353; Const. "In eligendis" of Pius IV, 9 Oct., 1562). The usage still continues and consists chiefly in a novena of Masses for the departed. A rescript of the Sacred Congregation of Rites (22 Apr., 1633) informs us that such novenas of mourning, officia novendialia ex testamento, were generally known and allowed in the churches of religious (Decr. Auth. S.R.C., 604). They are no longer in common use, though they have never been forbidden, and indeed, on the contrary, novendiales precum et Missarum devotiones pro defunctis were approved by Gregory XVI (11 July, 1853 [sic]) and indulgenced for a confraternity agonizantium in France (Resc. Auth. S.C. Indulg., 382)."
"Novena." The Catholic Encyclopedia. Vol. 11. New York: Robert Appleton Company, 1911. 20 Feb. 2016<http://www.newadvent.org/cathen/11141b.htm>. Emphasis mine.