In the original Greek myth, Pandora’s container was a jar, not a box. Hesiod calls it a pithos, a large storage vessel used in the ancient Greek world.
The familiar phrase “Pandora’s box” arose through a translation tradition. The Renaissance scholar Desiderius Erasmus translated the Greek vessel into Latin as pyxis, meaning a box or small container, and that wording helped establish the expression used in many modern languages.
A pithos was generally much larger and more substantial than the boxes pictured in later illustrations. Such jars could store grain, oil, or wine, so the ancient image was closer to opening a large storage vessel than lifting a lid from a small treasure chest.
The myth’s central action remains the same in later versions: Pandora opens the container, and troubles spread into the human world. The “box” wording is therefore traditional but not the earliest physical description.