In "Ode on a Grecian Urn," John Keats uses imagery to describe the pictures on the sides of the titular urn. Rather than present the reader with a plain list of images, he goes through each image in detail, using words that arouse certain sentiments to better capture how the urn is making the speaker feel. In fact, he leaves much up to the imagination. For example, the reader is told that the young lovers are beautiful, but we are never given what they are wearing or what specific features make them beautiful. The effect of the imagery is more impressionistic than detailed: the speaker's descriptions deal more with mystery and an astonishment at how long the beauty of the images have persisted than anything else.
The astonishment of the speaker is plain in descriptions such as the following:
Who are these coming to the sacrifice?
To what green altar, O mysterious priest,
Lead'st thou that heifer lowing at the skies,
And all her silken flanks with garlands drest?
What little town by river or sea shore,
Or mountain-built with peaceful citadel,
Is emptied of this folk, this pious morn?
The rapid-fire questions paint the reader a picture of the urn's images more than a straightforward description might. Because the imagery is presented in the form of a question, the speaker's astonishment is better emphasized, lending a mystique to the imagery as well. The figures become more fascinating because of what is not known about them such, as their original context.
Note also the predominance of nature in the imagery. The "green altar" and the sacrificial cow dressed with flower garlands evoke a world in which nature is more emphasized in daily life. The image of the musician beneath the eternally full trees also evokes this quality.
Keats sometimes uses oxymoron as well to get the imagery across. At one point, the speaker calls the urn a "Cold Pastoral," a term which delineates both the remoteness of the images and the idealized countryside setting. It gives the reader an impression of unreachable perfection.