What metaphors are used in Ode on a Grecian Urn by John Keats?

The poem opens with three consecutive metaphors: the implied, rather than directly stated, comparisons between the urn the speaker is viewing and, respectively, a "bride of quietness," a "foster-child of silence and slow time," and a "Sylvan historian," Of these, the last is perhaps easiest for the reader to immediately comprehend. Ancient Grecian urns were commonly illustrated with scenes or subjects that varied depending on the era and style in which a given urn was created.