This paper was initially conceived at the Italian Academy for Advanced Studies in America at Columbia University during the spring semester of 2008 (see hereby an abstract of the working paper presented there). Now the entire version has been published by Viator - journal of The Center for Medieval and Renaissance Studies, University of California, Los Angeles - and it is available on-line at:
http://brepols.metapress.com/content/0354rp8221q11126/?p=8beb5af38cf64688b905373d1390b213&pi=10