Ecclesia Mediolanensi celebrari coeperunt; cujus celebritatis devotio
usque in hodiernam diem, non solum, in Ecclesia Mediolanensi verum per
omnes pene Occidentis provincias manet."

But the question arises, when did Rome introduce hymns into her liturgy?
The learned Jesuit, Father Arevalo, held that the Roman Office had hymns
as an integral part from the time of St. Ambrose, and he called the
opinion of those who held that they were of later introduction an
inveterate error, _errorem inveteratum (Hymnodia Hispanica_ XVIII., n.
95). The introduction of antiphonal chanting was introduced into Rome at
the time of St. Ambrose and liturgical hymn singing, too, was
introduced about the same time. This we know from the Milanese priest
Paulinus, St. Augustine, Pope Celestine I., and Faustus, Bishop of Riez.
But formal, official and systematic hymnody was not introduced in Rome
until centuries after the death of St. Ambrose. Mabillon (Suppl. ad IV.
lib de div. off. Amalarii, t. 11) and Tomasi (In annot, ad Resp. et
antip. Rom. Ecc.) place the date of the introduction of hymns into the
Roman liturgy, in the eleventh or twelfth centuries. But scholars now
agree that hymns were formally recognised in the liturgy of Rome in the
latter half of the ninth century. "To judge of what Amalare of Metz
says, there was no sign of it at the beginning of the ninth century, but
from the middle of the same century onwards hymns must have been
introduced into the Office used by the Churches of the Frankish empire,
and shortly afterwards in Rome" (Baudot, _op. cit._, pp. 67-68). Wilfrid
Strabo agrees with Amalare. Rabanus Maurus testifies that hymns were in
general usage in the second part of the ninth century. (Migne, Pat. Lat.
clx. 159, cxiv. 956). This is the opinion of Gueranger, Pimont, Blume
and Baumer.

Dom Gueranger explains why Rome, the mother and mistress of all the