In Hesiod’s version of Pandora’s myth, the container was a jar, not a box. The Greek word is pithos, which commonly referred to a large storage jar.
The familiar phrase “Pandora’s box” developed through a translation history. In the sixteenth century, the Dutch humanist Erasmus translated the Greek pithos into the Latin pyxis, meaning a box or small container. That wording helped establish the expression used in English and many other languages.
Hesiod’s Works and Days says that Pandora opened the container and released human troubles into the world. The ancient text does not describe the object as the small hinged box shown in many modern illustrations.
The jar-versus-box distinction is one of the best-known differences between the original Greek myth and its later reception. “Pandora’s jar” is more faithful to Hesiod’s wording, while “Pandora’s box” remains the standard modern idiom.