Discuss political gains and losses through ancient events, as well as the king's behavior (fatuity and incompetence, etc. ); Admire the previous dynasty and take history as a mirror; Express your feelings by reciting history (often the pain of national subjugation and the short life).
Images, this is more, historical figures, mountains and rivers, according to the poem is different.
Commonly used techniques include allusions, metaphors and comparisons, among which metaphors are more common.