In 'The Merchant of Venice', Portia's suitors must choose from three caskets. Her late father designed the test to ensure that whoever married her valued character over wealth or appearance. The caskets are made of gold, silver, and lead, and each bears a cryptic inscription.
The Prince of Morocco chooses gold because its message promises what many people desire. The Prince of Arragon chooses silver because he believes he deserves Portia. Both choose incorrectly. Bassanio selects the lead casket, whose warning asks the chooser to risk everything, and finds Portia's portrait inside.
The casket plot comes from older romance traditions, including a story in the medieval collection 'Gesta Romanorum' and material in Giovanni Fiorentino's 'Il Pecorone'. It is separate from the play's other major plot: Antonio's bond with Shylock and the famous pound-of-flesh trial.
A common mix-up is remembering the caskets as boxes of different jewels. Shakespeare specifically identifies their metals as gold, silver, and lead, with only one correct choice.