Classical poetry is divided into four-character poems, five-character poems and seven-character poems.
Four-character ancient poems first appeared, such as The Book of Songs.
Five-character ancient poems matured in Han Dynasty and seven-character ancient poems matured in Tang Dynasty.
Yuefu poetry is also an ancient poem.
Modern poetry was mainly formed in the Tang Dynasty, in which even the sentences in ordinary poetry rhymed. The third sentence of the sonnet doesn't rhyme. In addition, the rhyme couplet and the neck couplet must be right, and the first couplet and the last couplet can be right.