The chapter archive of the Basilica of Sant’Ambrogio was founded more than 900 years ago, when, shortly after the year 1000, the canons organised themselves into a community that was responsible for officiating at the church. Alongside modern and contemporary documents concerning the more than sixteen centuries of Sant’Ambrogio’s history and its restoration over the ages, the archive preserves fifty-five parchment volumes dating between the ninth and eighteenth centuries, a few manuscripts on paper with liturgical content of importance for understanding the Ambrosian rite,