Hesiod actually describes a jar in the original Pandora story.
The Greek word is pithos, a large storage jar used in the ancient Mediterranean world. In Works and Days, Pandora opens this vessel and releases the troubles kept inside it. The earliest surviving Greek account therefore does not describe a small box with a hinged lid.
The phrase “Pandora’s box” became standard later because of a translation choice. The Renaissance humanist Erasmus translated pithos into Latin as pyxis, a word meaning box or small container, in his influential retelling. That wording helped establish the modern expression in European languages.
The traditional phrase is now so familiar that “Pandora’s box” is not considered an error in ordinary English. Still, the distinction matters when discussing Hesiod’s text: the ancient object was a large jar, and the famous English title reflects later reception rather than the original Greek wording.