Four Ages of Poetry is the title of Thomas Love Peacock's satirical essay about the changing place of poetry in society. In it, Peacock divides literary history into four supposed stages-iron, gold, silver, and brass-to mock the idea of fixed poetic progress and to argue, playfully but sharply, that poetry declines as civilization becomes more practical and commercial.
Example
Peacock's Four Ages of Poetry treats poetry's history as a comic descent:
iron, gold, silver, brass
-each age named for a material, not a muse.