The Greek container Pandora opened was a pithos, a large storage jar.
The earliest surviving literary account, in Hesiod’s Works and Days, describes a pithos rather than a small box. A pithos was a substantial earthenware vessel used in ancient Greece for storing commodities such as grain, wine, or oil. Its size and practical purpose make it very different from the compact box shown in many modern illustrations.
The “box” wording became standard through a long translation history. The Renaissance humanist Erasmus used the Latin term pyxis, meaning a box or small container, when translating the myth. That choice helped establish the familiar expression “Pandora’s box” in European languages.
The traditional interpretation is therefore not that modern retellings are inventing a new object, but that the object’s form changed through translation and cultural adaptation. “Pandora’s jar” is more faithful to the Greek wording, while “Pandora’s box” remains the established English idiom.