Of course theres Toms site, which predated this one and which has lots of fun ephemera that you wont easily find elsewhere.
Oh yes, Nathaniel also did a little page, here: http://www.mondo-digital.com/caligula.html.
Then theres this very interesting and very detailed!
Despite the claim in this article, Im quite sure that all 160,000m of negs were never kept at Technicolor Roma. Half of the negs and most of the scratch track seem to have vanished, which I rank as a tragedy equal to the destruction of the bulk of Stroheims Greed and the destruction in its entirety of Harry Langdons Heart Trouble (though Im certain that rogue prints of both those movies survived for at least several decades and may still be lingering somewhere in forgotten vaults, probably in rusty cans whose labels have all fallen off).
We should also mention Alberto Farinas 1993 graduate thesis at the Università degli Studi di Roma La Sapienza,
Lopera cinematografica nella giurisprudenza. Chapter 1 is called
produttore e il diritto morale del regista,
and it deals in large measure with Caligula.
Unfortunately, it omits some crucial portions of the story, which creates some confusion,
but it is nonetheless intriguing
and Im really surprised that anybody (other than me) would know about this topic.
Also, it at long last explains something I never understood,
namely, the legal status of a film director in Italy,
which is not employee or independent contractor,
Other than those? Oy. Not much. You can spend weeks, nonstop, hammering away relentlessly through every online search engine, and everything you find, combined, will not contain the info you will learn in the above few links. Yes, the situation really is that sad. What you will find online is misinformation, disinformation, blustering opinions, and blundering nonsense. Thats all thats out there, folks. If you know differently, please inform us. Since so few people have ever been interested in the topic, Im pretty confident that our book will sell all of three copies if were lucky.