In Greek mythology, Hesiod said Pandora opened a jar, not a box.
The Greek word in Hesiod's Works and Days is pithos, a large storage jar used in the ancient Mediterranean. Such jars could hold grain, wine, oil, or other materials and were often substantial household or agricultural containers. Hesiod's story places the evils of human life inside this vessel.
The expression “Pandora's box” became standard much later. The sixteenth-century humanist Desiderius Erasmus translated the Greek vessel using the Latin word pyxis, meaning a box or small container. That influential choice helped establish the wording used in many modern languages.
The distinction matters because the original image is not a small hinged box but a large jar. Some later artworks nevertheless show Pandora opening a compact box, reinforcing the familiar phrase. “Pandora's jar” is more faithful to Hesiod's surviving wording, while “Pandora's box” remains the established idiom.