The Extended Metaphor.......

Metaphors are very effective ways of developing ideas in poems; one special form, the "extended metaphor," can be particularly effective in certain situations. An extended metaphor is a comparison that provides the basis for an entire poem or for a lengthy section of a poem; its value lies in keeping the reader's attention focused on a single clear image while at the same time allowing the writer to develop a number of different aspects of an idea.

For Example: "Coming To" summarizes the life of that poem's speaker:

Like a steel drum

cast at sea

my days,

banged and dented by a found shore of

ineradicable realities,

sandsunk, finally, gaping,

rustsunk incompass grass.