The emperor retreated to the inner palace and stopped attending to state affairs.
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Du Mu's (杜牧) Tang poem 《泊秦淮》 - 商女不知亡国恨，隔江犹唱后庭花 - uses 后庭花 'rear-courtyard flower' to refer to the decadent palace song that became a metaphor for a fallen dynasty's negligence. The slang anatomical sense is modern and informal.
