Baudolino, Umberto Eco
The story of a peasant who rises to power when he's taken under the wing of Frederick Barbarossa, adopted in all but name.
A story full of inextricable ambiguities because Baudolino's special talent is to lie persuasively, and he constructs a tapestry of complex, involuted lies, mostly concerning the dazzling kingdom of Pester John to the East, which is already part of the mythic fabric of Europe. Therefore he and four collaborators who help build up the story half believe it already, and come to believe it more the more they fill in the outline and the shape in detail--the shape of a perfect kingdom and therefore impossible for imperfect men to conceive unless it really exists. So Baudolino, inflamed with a passion to journey there, infects Barbarossa with the same desire, which--though it never brings them near Prester John's kingdom if any--radically alters Barbarossa's course in life and the destony of many his path, and sword, crosses.
Is the Crusade against Saladin he undertakes late in life decent or wise? He is far more scrupulous than some of the the thugs who've typically led crusades in the previous two centuries, but Saladin has ruled--except for these bloody crusader wars that keep interrupting him--with a tolerably even hand over a mixed population seething at its extremes with mutual hostility. He's maintained religious tolerance--even toward Christians in spite of all these outside agitations by the tribe trying his patience. Barbarossa has some of the same qualities except for a tendency to fall into indiscriminate--all right, semi-discriminate--massacre when he feels his will has been too grievously crossed. Should he conquer and depose Saladin, would the people of Jerusalem consider it a fair trade? And mark this: war upon Saladin isn't even his main intent, it's the pretext required to get his soldiers moving. The main purpose of his quest is to pass through to the Eastern kingdom of Prester John, to return to him the Grasal or Grail which some unscrupulous knave has abscounded with from that magnificent country.
And this Grasal is what when it's at home? The wine bowl Baudolino's father was drinking from on his deathbed, which a remark of his father persuaded Baudolino was much likelier to resemble the Grasal than the cliche gold cup encrusted with gems and lapis lazuli he'd previously conjured. And if this was likelier to be the sort of vessel Christ drank from, what then? Surely it was likelier the simple drinking bowl of a poor carpenter's son would pass down the centuries from peasant to peasant than from noble to noble? He already half believes the tale when he presents the vessel to his adoptive father. He is still more persuaded when his intimates at court, worldly nad sophisticated counsellors all, instantly believe the story he conjures. Such men would scarcely be so gulled by a transparent fraud! Net result? another holy war of dubious provenance. Humankind should at last outgrow them.
I'm not worried that this detailed account of one passage qualifies as a spoiler, because the book teems with incidents as lively and as parabolically rich. It's generally axiomatic that a book over five hundred pages, even a very fine one, will have passages that could be trimmed without conspicuous loss, but there are exceptions.