The 'mistake' was made by a sixth century monk known as Dionysius Exiguus or in English Dennis the Small, the 85-year-old pontiff claims in the book 'Jesus of Nazareth: The Infancy Narratives', published on Wednesday.

"The calculation of the beginning of our calendar – based on the birth of Jesus – was made by Dionysius Exiguus, who made a mistake in his calculations by several years," the Pope writes in the book, which went on sale around the world with an initial print run of a million copies.

"The actual date of Jesus's birth was several years before."
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Which Popes were infallible, the Pope now or the Popes that agreed with the later birth date?