Factual error: Contrary to what the movie states, priests can be elected Pope - they are simply elevated to the rank of Bishop before taking the office.
Suggested correction: Him being only a priest was simply an excuse not to elect him. Those who did not want him to be pope were trying to find any reason to keep it from happening.
Any baptized Catholic male can be elected pope, although it has only happened once. Pope John XIX in the 11th century was a layman, ordained after his election.
Factual error: In the scene where Vetra is taken to examine the body of the deceased pope, the corpse is exposed after the marble slab and the lid of the casket is removed. In reality, papal funerary protocol requires the body to be triple-sealed. It is first placed in a coffin of cypress wood (to symbolise humility), and is then hermetically sealed in a zinc coffin to slow down decomposition. Finally, the zinc coffin is then placed inside of an oak coffin before being interred beneath the marble slab.
Factual error: When Langdon arrives at piazza del Popolo and drives over the square, the church (Santa Maria del Popolo) is at his left side. But in real Rome, the church is at the right side.
Factual error: The Fontana dei Quattro Fiumi, where the fourth cardinal is taken to be executed, is nowhere near as deep as it's depicted in the film. In reality it's only little more than a foot deep.
Factual error: The College of Cardinals debate whether or not to allow Father McKenna into the papal election as a candidate via election by acclamation. That process of election was abolished by Pope John Paul II in 1996; the secret ballot method is the only legal means of electing a Pope.
Factual error: In the scenes in Piazza Navona where the fourth Bishop is nearly drowned in the Fountain of the Four Rivers, the fountain is easily approached by car and on foot without any barriers. The real fountain has a railing around it of stone posts connected by long, oval-shaped iron rings and bars.
Factual error: The text in the Archimedes document was in English, but it was modern English. I am also fairly certain that the font picked had Serifs that were not used until the 20th century (at least they picked a variety of Times ROMAN).
Factual error: It is stated by Langdon that after the Pope's death, but before the successor is chosen, that the Camerlengo would become the head of the Church. This is incorrect. The Camerlengo would become Vatican City's acting head of state, however, the Church's leadership would actually be the College of Cardinals.
Factual error: Father McKenna is a simple priest and holds the post of Camerlengo, however the Camerlengo is always a Cardinal.
Factual error: In the beginning of the movie, we saw the Ring of the Fisherman of the dead pope, inscribed with his name: "PIUS XVI". However, the inscription should be done in Latin style, which uses "V" instead of "U". Thus the correct inscription should read "PIVS XVI". The Latin style of writing is evident in the Ring of the Fisherman that is worn by the real, currently reigning pope, Benedict XVI, which is inscribed "BENEDICTVS XVI".
Factual error: Langdon says Air Water Fire and Earth are fundamental scientific elements. That's not true. The "five elements" are philosophic, not scientific. (00:20:25)
Factual error: The size of the chamber in the Vatican archives is roughly 15x10x5 meters. That's equivalent to 750,000 liters of air. Even if we divide it in half to account for the furniture and take off another 25% to account for under-pressurization, that still leaves 280,000 liters of air. Two men would consume a maximum of 20 liters per minute, if they were hyper-ventilating. That's 233 hours worth of air, or almost ten days. Langdon and the security guard were trapped there for less than twenty minutes in all.
Factual error: At 1:37:15 the message received on the laptop instructs the villain to find his final payment in the Volkswagen located "N/E corner Via Giulia." When he flees Langdon he does so on the Passetto which runs east toward the Vatican, and he scales off the wall a short time/distance later to find the car. Via Giulia is actually south and across the Tiber river from the Castel Sant'Angelo. The villian would never have reached Via Giulia going on the Passetto or in that amount of time. (01:37:15)
