Ambrosian processions to the baptisteries
Terence Bailey
Idiosyncratic to the Milanese liturgy were processions after Matins and Vespers two ancient baptisteries of St John Baptist Stephen. These processions, held throughout year except in Holy Week, provided with a very large repertory antiphons (psallendae). The observances are documented Ambrosian antiphoners, Manuale, ordinal, but answer some important questions left unanswered these books has required detailed analysis comparison evidence that is certain respects contradictory.
Plainsong & Medieval Music