The Carry On movies are something of a British institution. Starting with Carry On Sergeant in 1958, originally they were comedies about a group of men pulling together in the face of adversity and in an attempt to get the girl, but over the years the plots devolved and the sex elements increased until the series petered out with the erotic Carry On Emmanuelle in 1978 and the failed attempt to reboot the series with Carry On Columbus in 1992. In between, however, the series produced some comedy classics (Carry On Up The Khyber, Carry On Matron) as well as some real stinkers (Carry On England). Carry Ons are characterised by two-dimensional characterisation, women walking around with their stomachs sucked in and breasts thrust out, extremely camp men chasing after said women and jokes at about the humour level of a Christmas cracker.
Carry On Cleo was one of the best (the films were often at their best when spoofing earlier films - Carry On Henry, a spoof of Anne of the Thousand Days, is another good one). Cleo also benefitted from being able to use leftover costumes and sets from Cleopatra - Sid James wears Richard Burton's costume throughout. I read a review of Cleopatra once - I'm afraid I can't remember where, I think it was Empire or Total Film - that suggested the best way to enjoy Cleopatra was to skip it and watch Carry On Cleo, which is shorter and funnier.
This is an example of Classics via Shakespeare, and much of the humour and the representations of Romans and Egyptians in this film stems from Shakespeare, rather than from Roman history. There's a running gag in which Caesar starts to make a speech, gets as far as 'Friends, Romans - ' and gets cut off by someone nearby hissing at him 'and Countrymen!'
As far as historical inaccuracy goes, I think the easiest thing is just to say, if you want to know what actually went on between Caesar, Cleopatra and Mark Antony, have a look at Wikipedia - though all the usual caution must be advised. If you have time, various primary sources including Appian, Plutarch and Suetonius are online at Lacus Curtius. With the exception of the eventual assassination of Caesar at the end, none of the events depicted in the film ever actually happened. Caesar and Mark Antony did both have affairs with Cleopatra, who had one son by Caesar and two children by Mark Antony, but not both at once.
Carry On Cleo opens, as usual in these films, with The Bit With The Writing, but in this case, the Writing simply assures us that, although the story is based on real people and events, 'some liberties have been taken with Cleopatra'.
The British are living in caves. I really hope I do not have to point out that this is less than historically accurate! It does emphasise nicely the difference in culture and technological achievement between the British and the Romans, but on the other hand, these are the descendants of the people who built Stonehenge, so suggesting they still haven’t invented the wheel by the 1st century BC is going a bit far. Our hero, the unforuntate Hengist Pod, has memorised his attractive and but unpleasant wife's nagging rant.
The Carry On team became something of a repertory company, with parts divided between regular actors, and for this movie, the part of Julius Caesar has been allotted to Kenneth Williams (his first line in the film being 'Oh, I do feel queer'), while Sid James plays Mark Antony. As a result, we have a Caesar who is very effeminate (though he does spend half the movie chasing girls, as is traditional for Carry On). The problem is that he can barely control his own household, let alone an army. It’s an unusual view of Caesar, and much of the humour (and the plot) comes from seeing familiar scenes and hearing familiar lines delivered in a very unfamiliar way. It should be noted that there were all sorts of rumours going around about Caesar’s private life in antiquity, so for all we know, it could be closer to the truth. Other regulars include Charles Hawtrey as Caesar's father-in-law, Joan Simms as his wife Calpurnia, Jim Dale as Horsa and Kenneth Connor as Hengist.
Carry On movies are always full of terrible, terrible puns, and the one about coming ‘hot-foot’ from Rome is one of the worst. I do like Caesar’s explanation that he has caught ‘Astinkin-cold’ though. The reason they all find Gloria from Bristol so funny, by the way, is that ‘bristols’, in cockney rhyming slang, mean breasts (Bristol City = titty). A lot of the jokes in Carry On films are unintelligible to non-Brits, and Caesar's joke about how he didn't even get his XI plus is becoming increasingly out of date in Britain as well (the eleven-plus exam is taken by students trying to get into grammar schools in Britain, including me some years ago, when I was going to the first of my two grammar schools). Anachronistic jokes aplenty flow when we get to Rome, my favourites being ‘Marcus and Spencius’ the merchants and poor Horsa getting branded for an owner named Willa Claudia (WC, ‘water closet’ in Britain stands for ‘toilet’). The terrible jokes are not restricted to English either
This is the best quality picture I could find of the Carry On view of the Vestal Virgins. These don't seem quite to have understood the meaning of the 'virgin' part.
As they go in, Horsa says they should pretend to be eunuchs and Hengist rhetorically asks what they've got to lose. Groan.
This is where Kenneth Williams, pursued by a murderous bodyguard, yells 'Infamy! Infamy! They've all got it in for me!' If you are at a Classics conference in the UK and everyone randomly starts yelling this line over dinner, this is where it's from. It is followed a little later by 'I came, I saw, I - conked out'.
Horsa kills all the guards and runs away, leaving Mark Antony to find Hengist, sword in hand, surrounded by dead conspirators. Hengist is made Caesar's bodyguard and Mark Antony is sent to Egypt to kill Cleopatra and put Ptolemy on the throne. He decides to do it the other way around, as he finds Cleopatra rather more attractive than Ptolemy.
At the end of the film, we see everyone living happily ever after - Hengist having placated his wife using the viagra, Horsa married to Gloria, Mark Antony and Cleo living in the bath - except for Caesar, who is stabbed to death by Brutus, giving up on his final speech when Brutus reminds him to say 'countrymen'.
The Carry On movies are much more valuable as evidence for British culture in the 1960s than anything else, and Carry On Cleo has a lot more to do with mid-twentieth century sexual stereotypes than anything relating to Classics. Depending on your sense of humour, it can be very funny. It plays on the best known elements of the ancient world - the might of Rome, the love affairs of Cleopatra, the unpopularity of Britain from a Roman point of view. History is thoroughly twisted out of all recognition, but Rome does much better than native Britain, where, in the world of Carry On, a man's mother-in-law can still be eaten by a brontesaurus in the 40s BC. The film assumes that the audience are at least familiar with Shakespeare's plays Julius Caesar and Antony and Cleopatra - without this familiarity, the jokes do not work so well. On the other hand, it is the elements of Shakespeare and of the earlier film Cleopatra that give the film its plot and structure, making it one of the better Carry Ons, and certainly one of the glossiest in terms of it's look. I'm very fond of it, though, as I watched Carry Ons a lot as a child, it has great sentimental value attached to it for me - I'm not sure friends I've shown it to have been quite so enthralled...