Rome = The Vatican

Vatican Intelligence and Espionage = The Entity (formally Holy Alliance)

http://catdir.loc.gov/catdir/toc/ecip0821/2008025769.html

Link take you to the table of contents and overview of a book titled

The Entity: Five Centuries of Secret Vatican Espionage

https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/vol.-54-no.-4/the-intelligence-officer2019s-bookshelf.html

The C_A refers to this book in their Intelligence Officer's Bookshelf