We only have 4 hymns that we know conclusively come from the pen of St. Ambrose, because the writings of his son St. Augustine attest to them by name. Many others bear his name but are not definitely Ambrosian in authorship.
However, I like to think that the beautiful tribute to an early virgin martyr, Agnes Beatae Virginis, usually attributed to St. Ambrose, is his. It has a certain clarity and declarative vigor that sounds like him. Here is my translation.
The blessed virgin Agnes flies
back to her home above the skies.
With love she gave her blood on earth
to gain a new celestial birth.
Mature enough to give her life,
though still too young to be a wife,
what joy she shows when death appears
that one would think: her bridegroom nears!
Her captors lead her to the fire
but she refuses their desire,
“For it is not such smold’ring brands
Christ’s virgins take into their hands.”
“This flaming fire of pagan rite
extinguishes all faith and light.
Then stab me here, so that the flood
may overcome this hearth in blood.”
Courageous underneath the blows,
her death a further witness shows,
for as she falls she bends her knee
and wraps her robes in modesty.
O Virgin-born, all praises be
to You throughout eternity.
and unto everlasting days
to Father and the Spirit, praise.