* DawsonCasting: Because the series takes place over nearly eighty years, this is both played straight and later inverted with many of the same characters. Just to name a few major examples:
** Creator/DerekJacobi, aged 38, played Claudius from the age of 19 to his death at 63.
** Siān Phillips, aged 43, played Livia from the age of 34 to her death at 86.
** George Baker, aged 45, played Tiberius from the age of 18 to his death at 77.
** Margaret Tyzack, also aged 45, played Antonia from the age of 27 to her death at 73.
** Some examples where this is purely played straight include Creator/JohnHurt (aged 36) as Caligula from the age of 17 to his death at 28, Christopher Biggins (aged 28) as 17-year-old Nero, and Graham Seed (aged 26) as ''13''-year-old Britannicus.
* DyeingForYourArt: George Baker, who was in his early forties, went on a regime of diet and exercise so he could realistically play a young Tiberius. He managed to equal the weight he used to have when he was twenty-four. It sort of doubles as accidental EnforcedMethodActing (does that even exist?) as his tiredness and exhaustion from working out so much and eating so little actually made it easier for him to play an often frustrated and bitter character prone to mood swings.
* EnforcedMethodActing:
** On early episodes, Jacobi put a stone in his shoe so he would limp realistically. Once he got used to it, he didn't need the stone any more.
** Baker lost a lot of weight to play Tiberius, which also made it easier for him to realistically play the mood swings, as the amount of diet and exercise provoked a lot of that for him in RealLife.
** Because of the alleged curse that'd already claimed some lives, Brian Blessed was a bit anxious. While they were shooting Augustus' dying scene, there was a blackout. By the time they did the take, he was terrified he would actually die on set, so the terror in his eyes is authentic.
* HeyItsThatGuy:
** Claudius is [[Series/DoctorWho The Master!]]
*** Or, if you ''really'' want to be clever: "Hey! [[Theatre/{{Hamlet}} Claudius]] is playing Claudius!"
** Augustus is '''''BrianBlessed!!!'''''
** Livia is [[Film/{{Dune}} The Reverend Mother Gaius Helen Mohiam!]]
** Tiberius is Inspector Wexford.
** Caligula is [[Film/{{Alien}} Kane!]]
*** Caligula and Macro were definitely a couple at [[TheNakedCivilServant one point]].
** Aelius Sejanus is [[Series/StarTrekTheNextGeneration Captain Picard!]]
*** With Hair?!
** Macro is [[LordOfTheRings Gimli!]]
** Livilla is [[RockyHorrorPictureShow Magenta!]]
*** While Nero is another of the Transylvanians. Or, alternatively, [[{{Series/Porridge}} Lukewarm]].
** Martina the Poisoner is is [[{{Blackadder}} Nursie!]]
** Herod is [[Literature/BridgetJones Uncle Geoffrey!]]
** Julia is [[Series/MayToDecember Miss Flood!!]]
** When Claudius is hiding from the Praetorian Guard, he is found by [[Series/BoysFromTheBlackstuff Yosser]], whose sergeant is [[Film/AHardDaysNight Norm!]]
** Agrippina is [[Recap/DoctorWhoS25E3SilverNemesis Lady Peinforte]]!
** And pretty much every actor who turns up has appeared in at least one other BBC production. There's even a [[http://calapine.dreamwidth.org/459307.html Doctor Who/I, Claudius DRINKING GAME]].
** Castor is [[PiratesOfTheCaribbean Mr. Gibbs]], though [[IWasQuiteALooker you really wouldn't know it.]]
** Livia's slave in episode one is [[Series/AlloAllo Lieutenant Gruber]]!
** The British chieftain Caractacus in the final episode is [[Series/ToTheManorBorn Richard DeVere]]!
* {{Plagiarism}}: Not this work, but it turns out that Richard Condon plagiarized several passages from ''I, Claudius'' in ''TheManchurianCandidate''. This went unnoticed until a few years after Condon died.
* ThrowItIn: For Livia's dying scene, John Hurt suggested Caligula actually jumped in bed with her, as that would be more realistic for the character. They made the take, and he spontaneously kissed her full in the lips to emphasise the kind of degenerate person Caligula was (Livia was his great-grandmother).
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