The absence of liturgical books proper to the high-medieval Aquileian liturgy does not allow to know the antique music repertoire of this Church. Important information on some ritual peculiarities can however be deducted from the works of some writers, starting from St. Chromatius [Cromazio], the bishop († 407 ca.). Probably the successful achievement of one of the greatest poets/musicians of the Carolingian period is not only due to his personal genius, but also to the lively cultural milieu of his homeland, that is to say the palatine magister grammaticus who became patriarch di Aquileia in 787: Paulinus II († 802). Some of his compositions – among which the renowned poem Ubi caritas est vera – are still nowadays universally sung in the solemn church liturgy. The extant Friulian sources are late, and in the eleventh-twelfth centuries they witness the Roman liturgy employment in Friuli together with its music repertoire (the Roman-Frankish or Gregorian chant). In such an environment ties can be found with the centres of the Germanic world and, in a smaller quantity, with northern Italy, above all Verona, Venice, Padua. The liturgical music books of Friuli therefore reflect the role of hinge this territory had between the Germanic and the Italic worlds. An unequivocal proof of this hybrid situation is the sanctorale that witnesses the import of transalpine saints in the local divine office. Another phenomenon recognizable at a glance is the presence of two notational traditions that mirror the cultural hegemony now of one side, now of the other one. The oldest surviving sources – which date back to the period subsequent the year 1000 – are decisively in favour of a Germanic priority. This is not surprising if we consider that since the beginning of the eleventh to the half of the thirteenth century all the patriarchs of Aquileia had been noblemen of Germanic provenance. This fact is strongly reflected by the imposing presence of transalpine notation, specified in its details through the developments of the Sankt Gallen scriptorium. A survey of the sources also detects some stratifications evidencing the interlacement of various foreign traditions: in different periods they have enriched the local heritage, grown throughout the Roman liturgy. Beyond the books written in the Friulian area and either destined or employed in the communities of this territory, the study of the liturgical sources should not neglect the presence of the patriarchal liturgy witnessed in further areas, as well as the orally transmitted vocal repertoire. There is firstly need to check the liturgical books of the very wide territory submitted to the ecclesiastical jurisdiction of Aquileia: the patriarchal rite was spread much outer than the regional borders and it reached Lombardy (Como, Cremona) and Piedmont (Orta) in the west, while towards the east it influenced the liturgy of the Church of Hungary.
Liturgical books are essentially books for the divine office, but at the same time they are books of poetry, painting art, music, too: so as to reach the highest peaks of the artistic engagement; so as to make the liturgical book one of the most eloquent and faithful mirrors reflecting the life of a community.