The antiphonary of Bangor an early Irish manuscript in the Ambrosian library at Milan

Description

from this MusicSacra forum question "pre-Gregorian sacred chant in Ireland?":

Quæritur:

Dom Saulnier, O.S.B.'s Gregorian Chant: A Guide pp. 3-4 lists the following types of pre-Gregorian chant:
1. Beneventan (southern Italy)
2. Roman (city of Rome and its environs)
3. Milanese (northern Italy)
4. Hispanic (both sides of the Pyrenees)
5. Gallican chant(s) (in Roman Gaul, basically France)
But was there a pre-Gregorian chant as far west as Ireland?

Respondeo:
Catholic Encyclopedia , "Celtic Rite" §Hymns:

There are many native Irish hymns both in Latin and Irish. Of these, most no doubt were not intended for liturgical use, but rather for private reading, but a certain number were undoubtedly used in the services of the Celtic Church. In the "Liber Hymnorum" there are hymns by Patrick, Columba, Gildas, Sechnall, Ultan, Cummaim of Clonfert, Muging, Coleman mac UiClussaigh, Colman Mac Murchan, Cuchuimne, Oengus, Fiach, Broccan, Sanctam, Scandalan Mor, Mael-Isu ua Brolchain, and Ninine, besides a few by non-Irish poets. The Bangor Antiphoner adds the names of Comgall and Camelac to the list. Of the twelve hymns given in the latter, eight are not found elsewhere, and ten are certainly intended for liturgical use.

(The Sarum Rite was after Pope St. Gregory the Great, c. 590 A.D.)

David Hiley, Western Plainchant: A Handbook p. 483:

the expression 'Celtic church' is usually meant the church in Britain and Ireland until the time when Augustine of Canterbury (d. 604 or 605) and later churchmen brought Roman usages, which gradually supplanted Celtic ones. […] Almost no chant which can be considered authentically Celtic has survived.

Buckley, A. (2001). Celtic chant. Grove Music Online. Retrieved 24 Jul. 2020:

[…] the preface to the hymn Altus prosator in a manuscript of the Irish Liber hymnorum (IRL-Dtc 1441) where it is related that Gregory the Great (d 604) sent Colmcille a cross and ‘immain na sechtmaine’ (‘hymns of the week’).

The [7th cen.] Antiphonary of Bangor is a collection of hymns, collects and canticles for the Divine Office; […] it represents the most important manuscript for an Irish Office. […] The Antiphonary of Bangor is the only source for Hymnus quando cereus benedicitur (‘the hymn sung at the blessing of the candle’) […] Sancti venite (no.8) is the oldest recorded communion hymn.