Pope St Gregory I

"Saint Gregory made and ordained the song of the office of holy church, and established at Rome two schools of song, that one beside the church of Saint Peter, and that other by the church of Saint …More
"Saint Gregory made and ordained the song of the office of holy church, and established at Rome two schools of song, that one beside the church of Saint Peter, and that other by the church of Saint John Lateran, where the place is yet, where he lay and taught the scholars, and the rod with which he menaced them, and the antiphoner on which he learned them is yet there." – from the 'Golden Legend' of Bl. James of Voragine OP Stained glass from the Anglican cathedral in Southwark.
Source: Lawrence OP on Flickr