Imagery in Ode on a Grecian Urn
This stanza suggests the narrator is looking at a different side of the urn with a different aspect of the painting. The narrator specifically calls the altar “green” to tell the reader it is a visual image not a figurative altar. Now we understand sacrifice is another decoration on the urn, symbolizing that art is not simply eternal happiness, but also eternal pain.
Tempe is a valley in Greece known for pastoral lands of great beauty. Arcady indicates the ancient Greek state of Arcadia. Mentioning Arcadia and Tempe establishes the the old age of the urn as well as brings to mind images of rustic, idealistic beauty.