In Greek mythology, Pandora opened a jar, not a box.
The ancient Greek word pithos referred to a large storage jar, often used for grain, wine, or oil. In the myth, Zeus had the jar made or entrusted it to Pandora, and it contained the troubles that later afflicted humanity.
The word “box” became familiar through a sixteenth-century Latin translation by Erasmus of Rotterdam. Erasmus used the Latin word pyxis, meaning a small box, rather than preserving the original image of a large jar. That translation shaped the standard expression in English and many other languages.
The myth therefore has two layers: the ancient story describes a storage vessel, while the modern idiom says “Pandora’s box.” The distinction is a common point of discussion in classical mythology, although both versions refer to the same famous episode.