Nicene and Post-Nicene Fathers, Ser. II, Vol. III:
Jerome and Gennadius. Lives of Illustrious Men.: Caelestinus the bishop.

Chapter LV.

Caelestinus, 2667 bishop of Rome, addressed a volume to the churches of the East and West, giving an account of the decree of the synod against the above mentioned Nestorius and maintaining that while there are two complete natures in Christ, the person of the Son of God is to be regarded as single. The above mentioned Nestorius was shown to be opposed to this view. Xystus likewise, the successor of Caelestinus, wrote on the same subject and to the same Nestorius and the Eastern bishops, giving the views of the Western bishops against his error.

Footnotes

Bishop (Pope) of Rome 422, died 432.