In his excellent description and analysis of Walters MS 11, Dr. Leo F. Miller gives little or no attention to what is at times the most vexing problem a liturgical manuscript can present, viz., for what church was the codex written? He determines the predominantly Ravennate character of the ‘martyrologium’ prefixed to the sacramentary-missal which constitutes the body of the book, but in general hesitates to assign the manuscript to Ravenna itself, because ‘it contains none of the liturgical uses proper to that city's ancient liturgy, to which the people clung so tenaciously until they were abolished by Archbishop Julius della Rovere,’ and adds: ‘would a Ravenna calendar lack such great names as Peter Chrysologus and Iohannes Angeloptes?’ It will not be amiss, therefore, to look about for other clues which may help us solve the problem. An initial clue may, indeed, be said to stand out in the calendar itself: March 21. Natale S. Patris nostri Benedicti. This formulation, which is found normally only in Benedictine calendars, taken together with the proper mass for the feast of the saint on fo1.37, leaves little room for doubt concerning the character of the church for which the book was intended, even as the blessing of the weekly reader, inserted after the Canon of the Mass (fol.12r), clearly indicates that the book at one time served a monastic church. Our problem, therefore, is to identify the abbey or priory, if possible, and here again there exists an important clue. In the ‘Missa pro Congregatione In honore (sic) sanctae Mariae,’ St. Ambrose is mentioned in both collect and postcommunion, as he is also in the ‘Nobis quoque peccatoribus’ and in the embolism after the Pater noster. There can be no question that the saint mentioned in the two prayers—Defende, quaesumus and Copiosa—is normally the patron of the monastery, and that this particular mass-formulary has in this book been adapted for use in a church dedicated to the famous bishop of Milan. It would be interesting, therefore, to find in the province of Ravenna a monastery dedicated to St. Ambrose, so remote, too, perhaps from the metropolitan city as not to be obliged or inclined to keep all its local observances. Such a monastery did, indeed, exist—Sancti A mbrosii de Rancla (Ranclo; the modern Ranchio), situated about seven kilometers north-northwest of Sarsina, the episcopal city of the diocese to which it belonged, a suffragan see of Ravenna—and although no chronicle or annals, recounting the inner and outer history of the abbey would seem to be extant, the archives of the diocese, meagerly published, to be sure, do give us for the eleventh, twelfth, and thirteenth centuries an occasional glimpse of its fortunes, at times perhaps even more.