The owners of the British department store Marks and Spencer were alerted to a send-up of their store's name ("Marcus and Spencius") and associated use of the store's colours (green and gold) and called in their lawyers. Legal action was averted when it was explained that no slight against the store was intended, and the owners settled for an apology and a letter of explanation to be sent to a leading newspaper. This idea was later dropped, however, and the incident forgotten.
The film's producers lost a lawsuit brought against them by 20th Century-Fox after it was judged the movie poster, which parodied that of Cleopatra (1963), was so similar as to be a breach of copyright.
Caesar says he is unqualified for any job other than emperor because he failed his "XI Plus". The "eleven plus" exam, common in Britain at the time this film was made, was set to children aged ten or eleven to stream them and determine their educational future.
The motto "Nihil expector in omnibus" actually translates as "I expect nothing at all." The reason that many have failed to translate it is because Caesar wrongly [but intentionally] says "expectore" which has no meaning in Latin. It is a Latin/English pun/double entendre, like many of the English lines in the movie. It is supposed to be recognized as "No Spitting (expectorate) on the (omni) Bus." There is no need to know the actual Latin to understand it this way, although it is expected that some will be familiar with original. The humor comes from the way the language has changed, changing setting profound into something banal.
As with many "Carry On" films the movie was cut by the BBFC for an 'A' (now PG) certificate. This included the removal of double entendre dialogue lines, including "backward people", "ants in his pants", and referrals to mutes as "having them cut out". Also cut was a shot of Mark Antony (Sidney James) wriggling his legs on top of Cleopatra (Amanda Barrie) and a scene showing the exhausted Antony staggering from her bedroom. Although the latter scene was restored the rest of the cuts still apply to all releases of the film.
According to issue 15 of the "Classic Carry On Film Collection" magazine/DVD series, some interior sets in this film were from the play Caligula, and had been supplied by Victor Maddern, who bought them for £155 when the play closed, and loaned them for Carry on Cleo (1964) for £800.
The line of dialogue said by Julius Caesar (Kenneth Williams, "Infamy...Infamy.....they've all got it in for me!", became particularly well-known because of this movie. It has been voted as one of the all-time ever funniest one-liner jokes in a movie.
Although the script is credited to Talbot Rothwell, the most often quoted line ("Infamy, infamy, they've all got it in for me!") was supplied by the writing team of Frank Muir and Denis Norden, who had coined it for their BBC Radio comedy series "Take It From Here". Norden recalled that Rothwell asked their permission to recycle the line before using it in his script.
The voice-over narration in the film was a joke and was voiced by the esteemed E.V.H. Emmett, an important man of gravitas, who had done extensive vocal work for the Gaumont British News newsreels from the 1930s, 40s and 50s.
The contract for "Carry On" regular Kenneth Connor stipulated that his filming schedule would not clash with his performances in the London West End production of "A Funny Thing Happened On The Way To The Forum" starring alongside Frankie Howerd in which he was still performing in during the shoot. Within about a couple of years there would be a film version of that stage play [See: A Funny Thing Happened on the Way to the Forum (1966)].
One of the senators states in the senate that there has been a decline and that he doesn't need to tell the senate what that leads to - a fall! This is a humorous reference to Edward Gibbon's classic book "Decline and Fall of the Roman Empire."
Kenneth Williams was recalled for some dubbing to a line that the censor wouldn't allow though. Concerning the lack of women abroad, he originally commented to Joan Sims "They don't have them abroad you know, they're a very backward people there". Backward had to be changed to bashful due to it's homosexual connotations.
Before the last scene, the narrator says that Caesar will have to sell the Senate on "the idea of the wind of change." This is a reference to a famous speech made by British Prime Minister Harold Macmillan in 1961.
Some of the film's literal English language translations of its foreign language titles were "Ok, Cleo" (Belgium), "So, So Cleopatra" (Denmark), "Stop Your Chariot Cleo" (France), "Way to Go Cleopatra" (Portugal), and "Heroic Suckers in the Country of the Pharaoh" (Greece).
Cleopatra appearing from an unrolled carpet is based on accepted history. Most versions have Cleopatra being presented to Caesar in this unusual manner on his state visit, but the only historical account (by Cassius Dio) states that Cleopatra hid in the carpet to escape from Egyptian rebels under the command of her sister Arsinoe who were besieging her and Caesar in her palace.
During the movie Jim Dale takes out a number of Romans alone then makes a run for it, Sidney James comes in to catch Kenneth Connor dazed and wielding a sword who then passes out in front of him where Sid then uses the words "What A Carve Up". James and Connor had previously starred in the murder mystery No Place Like Homicide! (1961).
The movie's opening credits state that the film is "from an original idea by William Shakespeare". This "Carry On" comedy film utilizes for story elements two of Will's plays that were set in Ancient Times, "Julius Caesar" and "Antony and Cleopatra", with the film's Carry on Cleo (1964) title only specifically referencing one of the two plays (the latter).
The Latin expression said by Julius Caesar (Kenneth Williams) was "Nihil expectore in omnibus". The English meaning of it said in the movie was "No spitting on the public transport". In the film, the phrase was said to be Caesar's political slogan. Online Latin-English translators translate it as actually meaning: "There expectore all".
Barbara Windsor claimed in a TV interview that she was supposed to play Cleopatra, but she refused to wear a black wig for the film. When asked about it, Peter Rogers claimed Barbara was never considered to play Cleopatra.
When the filming of the Elizabeth Taylor epic of Cleopatra was abandoned at Pinewood the sets were left standing, it being cheaper than pulling them down for re- use. This allowed the Carry on team to move in and make full use of them. However when they tried to use an exact copy of the Cleopatra poster with the heads of Amanda Barrie, Kenneth Williams and Sid James replacing those of Elizabeth Taylor, Richard Burton and Rex Harrison Fox, despite huge financial losses in making their film and poor box office takings they still had enough financial clout to take court action over copyright infringement, which they won causing the Carry on poster to be changed.
The trivia item below may give away important plot points.
The first "Carry On" movie in which Kenneth Williams, portraying the character of Julius Caesar, dies. The second being his character of Thomas Cromwell in Carry on Henry VIII (1971). Although, in Carry on Screaming! (1966), his dead, but still animate, character perishes in a vat of boiling wax.