In Greek mythology, Pandora was originally said to have opened a jar. Hesiod’s Greek word is pithos, a large storage vessel, but later translations and retellings turned it into the familiar phrase “Pandora’s box.”
A pithos was a substantial ceramic container used in the ancient Greek world for storing goods such as grain, oil, or wine. In the myth, Zeus instructed Pandora not to open the vessel, but curiosity led her to do so.
When the jar opened, evils escaped and spread among humanity. Pandora shut it before everything inside had departed, leaving Hope behind. The exact interpretation of Hope varies, but its presence explains why the expression can suggest both catastrophe and a remaining comfort.
The “box” version became dominant through later translations and artistic traditions. Therefore, “jar” is the historically precise answer for the earliest surviving Greek account.