Linkblog, the blog of links everywhere!

In point of fact, the chant that was used in Gregory's time is now known as Old Roman, which barely survived into the era of musical notation, passing from one generation to the next by ear. In about the year 800, two centuries after Gregory's time, the Emperor Charlemagne sent to Rome for authentic liturgical books and chants. Singing teachers were dispatched from Rome to teach the Franks by ear, but they did not get along well and the Franks made major changes in order to adapt the chant to their taste and their ways of singing.

Old Roman Chant article on Wikipedia.