Keats’ engraving of the Greek Sosibios Vase, c. 1819. (Sources: Wikipedia; “Shakespeare Staging,” UC Berkeley). Critics agree that the urn in “Urn” was not intended as an exact representation of a particular object.
In addition, the Carlos Museum has a few beautiful artifacts from ancient Greece, including this krater (vase used to mix wine and water) and kylix (drinking cup). These containers all served ritual functions and represent mythical scenes, similar to the ones Keats describes. An urn would contain the ashes of someone wealthy and powerful. That morbid aspect, however, does not enter poem–or does it?