In the Greek myth of Pandora's Box, Pandora's container was originally called a pithos.
A pithos was a large storage jar used in ancient Greece for commodities such as grain, oil, and wine. The earliest surviving literary accounts of Pandora, especially Hesiod's works, describe a pithos rather than a box. The familiar “box” is the result of a later translation tradition.
The change is often associated with the Renaissance humanist Erasmus, whose Latin wording helped popularize the idea of a small container. His rendering used the Latin word pyxis, meaning a box or small chest, instead of the Greek pithos.
This distinction matters because the vessel in the original story was not necessarily portable or box-shaped. “Pandora's box” remains the standard English expression, but “Pandora's jar” is closer to the ancient Greek text.