Ambrose in the fourth century wrote hymns in a severe style, clothing Christian ideas in classical phraseology, and yet appealing to popular tastes. He had found a new form and created a new school of hymnody. St. Hilary of Poitiers (died 367), who is mentioned by St. Isidore of Seville as the first to compose Latin hymns, and Ambrose, styled by Dreves "the Father of Church-song", are linked together as pioneers of Western hymnody. Isidore, who died in 636, testifies to the spread of the custom from Milan throughout the whole of the West, and refers to the hymns as Ambrosian.
In uncritical ages, hymns, whether metrical or merely accentual, following the material form of those of St. Ambrose, were generally ascribed to him and were called "Ambrosiani". As now used, the term implies no attribution of authorship, but rather a poetical form or a liturgical use. To St. Ambrose himself scholarship gives fourteen hymns certainly, three very probably, and one probably.
The first actually to compose hymns was St. Hilary, who had spent in Asia Minor some years of exile from his see, and had thus become acquainted with the Syrian and Greek hymns of the Eastern Church. His Liber Hymnorum has not survived. Daniel, in his Thesaurus Hymnologicus mistakenly attributed seven hymns to Hilary, two of which were considered by hymnologists generally to have had good reason for the ascription, until Blume showed the error underlying the ascription. The two hymns have the metric and strophic cast peculiar to the authenticated hymns of St. Ambrose and to the hymns which were afterwards composed on the model.
Like St. Hilary, St. Ambrose was also a "Hammer of the Arians". Answering their complaints on this head, he says:
And St. Augustine speaks of the occasion when the hymns were introduced by Ambrose to be sung "according to the fashion of the East".
The rule of St. Benedict employed the term; and Walafridus Strabo notes that, while St. Benedict styled the hymns to be used in the canonical hours Ambrosianos, the term is to be understood as referring to hymns composed either by St. Ambrose or by others who followed his form; and, remarking further that many hymns were wrongly supposed to be his, thinks it incredible that he should have composed "some of them, which have no logical coherence and exhibit an awkwardness alien to the style of Ambrose". Daniel gives no less than ninety-two Ambrosiani, under the heading, however, of "S. Ambrosius et Ambrosiani", implying a distinction which for the present he cared not to specify more minutely.