Factual error: This movie tries as best it can to convince the viewer the action is happening in the states even though it was shot in Italy. (1) during a news report, the term 'his excellency the governor' is used which is used nowhere in the states. The rest of the newscast is equally odd. (2) the architecture is definitely 1950s Italy. (3) there is almost a complete lack of American automobiles; most of them are Fiats. (4) you can see Lebanese cedar trees everywhere trimmed in the Mediterranean style (tall and skinny). There are many more too numerous to go into.
Factual error: In a scene set in 1871, several newspaper articles get printed on Moe's face as he falls onto a printing press. Curly Joe reads that "AT&T is splitting two for one." American Telephone and Telegraph Company was founded in 1885.
Factual error: Fakrash is a genie who served under King Solomon and he himself says that he's been imprisoned for 3'000 years. Yet the whole aesthetics of his clothes, decoration, architecture is the stereotypical Arabian Nights one, which would be several centuries posterior to his times and almost as foreign to him as the present day one.
Factual error: In reality, Commodus did not die in the arena - he was strangled in his apartments in 192 A.D. by an athlete who was hired by a group of Senators conspiring against him.
Factual error: The radio Walter uses on the island has no apparent power source; we never see either batteries or a hand-cranked generator.
Factual error: Ma Tatum, while bemoaning Pappy's misfortune, sits herself on a burlap bag marked "Mash". Mash, the basic component of moonshine, is a semi-liquid, and couldn't be stored in a burlap bag.
Factual error: At the start of the excommunication scene, the monks are chanting Dies Irae, a thirteenth century Catholic poem, but St. Thomas Becket died in 1170, almost a century before the poem was written.