and a wise pastor, who
did so much for the welfare of mankind, he it was who also composed
this chant, which we sing in the Church and everywhere, with great
pains and with a complete knowledge of the musical art. He wished by
this means to act more powerfully upon men's hearts in order to arouse
and touch them; and in fact the sound of his sweet melodies has
gathered in the Churches not merely spiritual men, but also those who
are less cultivated and sensitive.

"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