St. Isidore of Seville (d. 636) and Pope Gregory the Great (d. 604) had an intellectual exchange facilitated in part by Isidore’s brother Leander (d. ca. 600), who preceded Isidore as bishop of Seville, had met Gregory in Constantinople, and to whom Gregory dedicated his Moralia in Job. Isidore’s writings and contemporaneous records of Spanish church councils make clear that the Old Hispanic Rite was already largely, though not entirely, formed in his day, much as we find it in the earliest surviving liturgical documents: the Oracional Visigótico (ca. 711) and the Antiphoner of León (ca. 900). This is a rite deriving from a great exegetical project in which liturgical chant formed only a part. Its starting points were the various translations of the Bible and the writings of the church fathers, especially Gregory and Augustine. From this an elaborate and systematic repertory of chant was formed in coordination with prayers, readings, and sermons. All of this speaks to deliberate composition by Isidore, Leander, and their colleagues rather than to the writing down of a long-standing oral tradition. Gregory surely knew about this activity in Spain. Is it likely that Gregory and his colleagues were not engaged in any such activity or that such activity in Rome took place so much later than it did in Spain? Perhaps there is a good reason why the chant created in Rome is called Gregorian just as the Old Hispanic Chant was much later called Isidorean. In the absence of Roman sources we may never know. But the Old Hispanic sources suggest that we ought to wonder.