Commentary Purg XXXII 136-141

In a sort of replay of the second calamity (the Donation of Constantine), the chariot is once again covered in imperial feathers.  The standard interpretation of these verses is that they refer to the grants of lands to the Church by two French kings, Pepin and Charlemagne, in the second half of the eighth century.

      The 'plumage,' which the poet suggests was 'offered perhaps with kind and innocent intent,' represents once again that which belonged to the empire by God's intent, and legally, in Dante's view, could not be surrendered to ecclesiastical authority, even though kings had chosen to do so.  See [Par XX 55-57], where a similar expression is used to indicate that Constantine had sinned grievously, if without meaning to do so.