Editors. "Cesare Borgia is imprisoned for refusing to submit to the new Pope". The Literary Encyclopedia. First published 01 November 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=14080, accessed 10 December 2013.]
Cesare Borgia is imprisoned for refusing to surrender the castles he had conquered in the Romagna to the new Pope Julius II. Once he has given up these possessions, he is freed again.