"I pray you not to allow yourself to remain in disagreement either with this Church, which is the chief head of religion, and from which no one wishes to stray, or with all those Churches of which we have spoken, if you love to live in complete peace and concord with the Universal Church. For if--which we do not believe--your aversion for our instruction and for the tradition of our holy Pontiff is such that you are not willing to conform in every point to our rite, both in chants and lessons, know that we will repel you from our communion; for it is fitting and healthful for you to follow the usages for which the Roman Church, mother of all and mistress of you, shows such great love and invincible attachment. For this reason we order you, under pain of excommunication, to conform in the Churches both in singing and reading exclusively to the order instituted by the Holy Pope Gregory and followed by us, and without fail to practise and sing it in future with the utmost zeal. For if--which we cannot believe--anyone shall attempt by any means whatever to turn you from the right path by leading you to a tradition other than that which we have just prescribed to you for the present and the future, we not only order that he be deprived of partaking of the Holy Body and Blood of our Lord Jesus Christ, but in virtue of our proper authority and that of all our predecessors, we decree that in punishment of his audacity and presumption he remain under a perpetual anathema."--(_Cod. Brit. Mus._, _add._ 8873, _fol._ 168.) Pope Leo, the author of this letter, had himself been a pupil at this same monastery of St. Martin. From thence also the priest John, the Precentor of St. Peter's, had set out 200 years before to teach the English the system of chanting and reading followed at St. Peter's. The above extract throws an important light on the progress of the Gregorian reform of the ecclesiastical chant. In the latter half of the ninth century a powerful monastery close to Rome had not yet adopted it. Compare with this fact the presence of the Ambrosian chant in the province of Capua in the middle of the eleventh century (Kienle, in _Studien und Mittheilungen des Benedictiner und Cistercienser-Orden_, 1884, _p._ 346), and the Ambrosian rubrics of various books copied a little later for churches at Rome itself (_Tomasi, Opp. vol._ vii., _pp._ 9 _&_ 10), and it will be seen how gradually the Gregorian books attained their universal supremacy. III.--Hildemar (between 833 and 850), author of a commentary on the Rule of St. Bennet, speaks of St. Gregory as the composer of the "Roman Office": "Beatus Gregorius qui dicitur Romanum Officium fecisse." (_Expositio Regula ab Hildemaro tradita_, _p._ 311, _Ratisbon_, 1880.)