Possibly written by St. Ambrose, this is a beautiful office hymn in honor of Ss. Peter and Paul.
http://www.chantcafe.com/2020/06/office-hymn-in-honor-of-saints-peter-and-paul/
http://www.chantcafe.com/2020/06/office-hymn-in-honor-of-saints-peter-and-paul/