Letter 120:13. Damian to young King Henry IV, A. D. 1065 or 1066, wherein Damian exhorts Henry to use his sword against the disturber of the Church’s peace, Cadalus, the bishop of Parma, the antipope Honorius II (d. 1072):
The Fathers of the Church, Medieval Continuation, 1998, Letters 91-120, Owen J. Blum, Irven Michael Resnick, trs., Catholic University of America Press, ISBN 0813208165 ISBN 9780813208169, vol. 5, pp. 393-394. http://books.google.com/books?id=Vlspdtjmhd4C&pg=PA393&dq=%22Let+that+ancient+dragon,+Cadalus,+take+note%22&hl=en&ei=QVpiTIjeIIG88gaFq-SVCQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDYQ6AEwAQ#v=onepage&q=%22Let%20that%20ancient%20dragon%2C%20Cadalus%2C%20take%20note%22&f=false