The History of the Kings of Britain

The History of the Kings of Britain was a book written by, obtained by Ezio Auditore da Firenze in the 16th century in Constantinople.

Summary
''A lively piece of pseudo-historical claptrap, the "History of the Kings of Britain" was credited as true history by far too many scholars untill well into the sixteenth century CE. Written four hundred years earlier, Geoffrey of Monmouth claims to have copied most of his data from an earlier source, but most modern scholars believe this to be a steaming pile of nonsense.''

Source

 * ''Assassin's Creed: Revelations