USUARDO. — Benedictine of St-Germain-des-Près (Paris), author of a martyrology, died around 875–77, on 13 January. Nothing is known of his origins. He was a professed religious in 838, when he signed a pact of prayers between his monastery and that of S. Remigio of Reims.
Charged with searching among the ruins of Valenza, sacked by the Moors, for the body of the deacon St. Vincenzo, principal patron of St-Germain-des-Près, U. went to Spain in 858, equipped with letters of recommendation from Carlo il Calvo; but he was able to bring back from Cordova only the relics of the martyrs Giorgio, Aureliano, and Natalia, which he deposited at Emant in the diocese of Sens, awaiting the opportunity, in 863, to restore them to the monastery of St-Germain, abandoned after the Norman expedition of 856. The account of the journey to Spain was written by the monk Aymon: De translatione ss. mart. Georgii etc. (PL 115, 939–60).

(from Acta SS. Iunii, VII, Anversa III, p. 517)
USUARDO - Martyrologium Uluardi, in the edition of G. B. du Sollier. The page reproduced contains the notices for 6 September, accompanied by the complete critical apparatus.
The collection of 875 soon spread beyond the Benedictine monasteries, to such an extent as to replace the other liturgical martyrologies. The manuscript texts were multiplied, without remaining free from additions, reworkings, and local adaptations; likewise the editions, from the editio princeps of Lübeck of 1475 to those of G. B. du Sollier (Antwerp 1714), republished in Acta SS. Iunii, VI and VII and in PL 123, 599-992; 124, 9-860, and that of Giac. Bouillart (Paris 1718). U.’s text formed the basis of the subsequent redactions of the Martyrologium Romanum, beginning with the official Roman edition of 1582 and that of 1584, produced under Gregory XIII according to the decrees of the Council of Trent.