The mistranslation of pithos, a large storage jar, as "box" is usually attributed to the sixteenth century humanist Erasmus of Rotterdam when he translated Hesiod's tale of Pandora into Latin. Hesiod's pithos refers to a large storage jar, often half-buried in the ground, used for wine, oil or grain.
It can also refer to a funerary jar.
Erasmus, however, translated pithos into the Latin word pyxis, meaning "box". The phrase "Pandora's box" has endured ever since.