A jar held the troubles released by Pandora in the earliest Greek version of her myth. Hesiod describes the container with the Greek word pithos, a large storage jar rather than a small wooden box.
The familiar expression “Pandora’s box” developed much later. In the sixteenth century, the humanist Desiderius Erasmus translated or adapted the story using the Latin word pyxis, meaning a box or small container. That wording helped establish the expression now common in English and many other languages.
Ancient Greek storage jars could hold grain, wine, oil, or other goods, so the pithos was a practical household object. The change from jar to box is therefore a translation history, not a detail in Hesiod’s original description. Modern illustrations usually follow the later box tradition.