The plot of Cymbeline is based on a tale in the chronicles of Raphael Holinshed and is ultimately part of the Matter of Britain, derived from the part of the Historia Regum Britanniae of Geoffrey of Monmouth about the real-life British monarch Cunobeline. Shakespeare, however, freely adapts the legend and adds entirely original sub-plots. Iachimo's wager and subsequent hiding-place inside a chest in order to gather details of Imogen's room derive from story II.9 of Giovanni Boccaccio's Decameron.
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