Jim, that is a fascinating remark (though it appears that the window in question was only one of several at S Denis from the Life of St. Benedict.) The relics of St. Benedict were in fact transferred to Fossés in 868; the relationships between Glanfeuil, Fossés and S. Denis were at that time very close. Members of the Rorigo family (a powerful Maine-based Frankish clan) appear to have been in control of all three abbeys in the mid and late 9th century. Moreover, late Carolingian kings were much interested both in Fossés and S. Denis .I don’t know how far into the future such close relationships were maintained..but I’m currently looking into the issue.