On 25 May, 1802, during the quest for the graves of Roman martyrs in the Catacomb of Priscilla, a tomb was discovered and opened; as it contained a glass vessel it was assumed to be the grave of a martyr. The view, then erroneously entertained in Rome, that the presence of such vessels (supposed to have contained the martyr's blood) in a grave was a symbol of martyrdom, has been rejected in practice since the investigations of De Rossi (cf. Leclercq in "Dict. d.archéol. chrét. et de liturg.", s.v. Ampoules de sang). The remains found in the above-mentioned tomb were shown to be those of a young maiden, and, as the name Filumena was discovered on the earthenware slabs closing the grave, it was assumed that they were those of a virgin martyr named Philumena. On 8 June, 1805, the relics were translated to the church of Mungano, Diocese of Nola (near Naples), and enshrined under one of its altars. In 1827 Leo XII presented the church with the three earthenware tiles, with the inscription, which may be seen in the church even today. On the basis of alleged revelations to a nun in Naples, and of an entirely fanciful and indefensible explanation of the allegorical paintings, which were found on the slabs beside the inscription, a canon of the church in Mugnano, named Di Lucia, composed a purely fictitious and romantic account of the supposed martyrdom of St. Philomena, who is not mentioned in any of the ancient sources. In consequence of the wonderful favours received in answer to prayer before the relics of the saint at Mugnano, devotion to them spread rapidly, and, after instituting investigations into the question, Gregory XVI appointed a special feast to be held on 9 September, "in honorem s. Philumenae virginis et martyris" (cf. the lessons of this feast in the Roman Breviary). The earthenware plates were fixed in front of the grave as follows: LUMENA PAX TECUM FI. The plates were evidently inserted in the wrong order, and the inscription should doubtless read PAX TECUM FILUMENA. The letters are painted on the plates with red paint, and the inscription belongs to the primitive class of epigraphical memorials in the Catacomb of Priscilla, thus, dating from about the middle or second half of the second century. The disarrangement of the inscription proves that it must have been completed before the plates were put into position, although in the numerous other examples of this kind in the same catacomb the inscription was added only after the grave had been closed. Consequently, since the disarrangement of the plates can scarcely be explained as arising from an error, Marucchi seems justified in concluding that the inscription and plates originally belonged to an earlier grave, and were later employed (now in the wrong order) to close another. Apart from the letters, the plates contain three arrows, either as adecoration or a punctuation, a leaf as decoration, two anchors, and a palm as the well-known Christian symbols. Neither these signs nor the glass vessel discovered in the grave can be regarded as a proof of martyrdom.
(Taken from Catholic Encyclopedia)