Rhythmic poetry was gradually perfected and finalized by people in the Tang Dynasty according to the embryonic form of Rhythmic Poetry in the Southern and Northern Dynasties. Common are five-character sentences and seven-character sentences. There are also very few four-character and six-character sentences. There are strict rules on the sentence pattern and the whole structure of rhythmic poetry, that is, the number of words, antithesis, rhythm, rhyme and stickiness. These provisions are the basic elements of metrical poetry.