In Hesiod’s account, Pandora opened a pithos, a large storage jar, before the object became known as a box.
The Greek word pithos refers to a substantial earthenware container used for storing commodities such as grain, oil or wine. Hesiod’s Works and Days does not describe the object as a small hinged box. The familiar English expression developed through later translation and artistic tradition.
This change is one of the best-known differences between the ancient myth and its modern wording. “Pandora’s box” is now an established idiom for an action that releases many unforeseen problems, so replacing it with “Pandora’s jar” would sound unfamiliar even though it is closer to the ancient text.
A pithos should not be confused with an amphora, which usually has two handles and a narrower shape, or a krater, which was used for mixing wine and water. Those are distinct vessel types from the large storage jar in the myth.