A Latin hymn to the Virgin Mary by St Hildegard of Bingen, written in the twelfth century, although it can be interpreted much more broadly than just as a simple hymn. The text of it (although not the original music) was most recently incorporated into Voices of Light, the oratorio by Richard Einhorn about St Joan of Arc. Note that it has some of the quirks sometimes seen in medieval ecclesiastical Latin (-e for genitive singular inflection, -ae, in classical Latin, for example). It runs:
O feminea forma, o soror sapientie,
quam gloriosa es!
Quoniam fortissima vita
in te surrexit
quam mors numquam suffocabit!
O feminine form, o sister of wisdom,
how glorious you are!
For in you has has arisen
the mightiest life
which death shall never stifle!