St. Ambrose, Father and Doctor of the Catholic Church, was Bishop of Milan from 374 to 397. He was born around 340, at Trier, Arles, or Lyons, and died in 397. Ambrose was descended from an ancient Roman family, which at an early period had embraced Christianity, and numbered among its scions both Christian martyrs and high officials of State. At the time of his birth his father was Prefect of Gallia, and as such ruled the present territories of France, Britain, and Spain, together with Tingitana in Africa. About the year 354 the father died, and the family moved to Rome. In 374, at the age of 35, Ambrose was consecrated bishop. In order to overcome the lack of an early theological training, he devoted himself to the study of Scripture and the Fathers, with a marked preference for Origen and St. Basil, traces of whose influence are repeatedly met with in his works.
Ambrose wrote exegetical, dogmatic, moral, and other texts. The exegetical writings, or commentaries on scripture, deal with the story of Creation, the Old Testament figures of Cain and Abel, Noah, Abraham and the patriarchs, and other subjects. Ambrose's work of interest here is his Hexaemeron (or Hexameron), a series of allegorical sermons on the six days of creation as told in the biblical book of Genesis. His commentary on the fourth day (creation of birds and fish) and fifth day (creation of land animals) influenced the later writers of the bestiaries and encyclopedias, who occasionally quote from him directly. Ambrose's stature as a Father of the Church ensured that his account of the creation of animals would be accepted as true.
[Adapted in part from the Catholic Encyclopedia]