In Hesiod’s original Greek account, Pandora’s troubles were held in a jar.
The Greek word in Works and Days is pithos, a large storage jar used for commodities such as grain, wine, or oil. Hesiod does not describe a small wooden box. The phrase “Pandora’s box” became standard much later because Renaissance readers and translators rendered the ancient container as a box.
The distinction matters because the modern expression is based on a translation history, not on the exact wording of the earliest surviving account. The jar is opened, releasing the evils that afflict humanity; hope remains inside when the container is closed again.
The jar is also not usually described as a specially decorated treasure chest. Ancient Greek pithoi could be very large, practical vessels. The familiar image of Pandora lifting a small box belongs mainly to later art, literature, and popular culture.