In Hesiod’s account, Pandora opened a jar, not a box.
The ancient Greek word used in the story is pithos, a large storage jar commonly used for agricultural products such as grain or oil. Hesiod’s Works and Days describes evils escaping from this container after Pandora removes its covering. The familiar phrase “Pandora’s box” arose later, rather than being the wording of the earliest surviving literary account.
The “box” became standard through a translation history associated especially with the Renaissance scholar Erasmus. In translating the Greek story into Latin, Erasmus used the word pyxis, meaning a small box or container, instead of pithos. That choice helped establish the expression used in many modern languages.
Art and popular culture usually depict a small decorative box, so the original jar is easily forgotten. The distinction matters because pithos was a substantial household storage vessel, not necessarily a portable jewelry box.