Aeterne rerum conditor. St. Ambrose. [Sunday Morning.] This hymn by St. Ambrose is received as genuine by the Benedictine editors….
The use of this hymn has been most extensive. In the Mozarabic Breviary (1502, f. 2) it is the hymn at Matins on the 1st Sunday in Advent, and generally on Sundays in Advent, Lent, Palm Sunday, Whitsun Day, &c.; in the Sarum, York, Evesham, Hereford, and St. Alban's, at Lauds on Sundays from the Octave of the Epiphany to Lent, and from the 1st Oct. to Advent; in the Worcester at Matins (so also some old Breviaries of the Benedictine Order (Daniel, i. g. 15); and in the Roman, for Sundays at Lauds, from the Octave of the Epiphany to the 1st Sunday in Lent, and from the S. nearest to the 1st of Oct. to Advent.
The text of this hymn is found in the Junius of the 8th century, No. xxv., and in two llth century manuscripts in the British Museum (Harl. 2961, f. 2186; Jul. A. vi. f. 19). In the Latin Hymns of the Anglo-Saxon Church, 1851, it is printed from a Durham manuscript of the llth century, and is given in the following works: St. Ambrosii Opp., Paris, 1836, p. 200; Daniel, i. 15, iv. 3; Trench, 1864, 243; Cardinal Newman's Hymni Ecclesiae, 1838, &c. Daniel and Trench are specially rich in illustrative notes. The variations in the Roman Breviary are also found in these works. [Rev. W. A. Shoults, B. D.]
Translations not in common use:—
7. O Thou Everlasting Maker. J. Banks, 1854.
--Excerpts from John Julian, Dictionary of Hymnology