Metre (poetry) of over some two-and-a-half millennia. Beginning with the earlier recorded forms: the Classic of Poetry tends toward couplets of four-character lines, grouped in rhymed quatrains; and, the Chuci follows this to some extent, but moves toward variations in line length. Han Dynasty poetry tended towards the variable line-length forms of the folk ballads and the Music Bureau yuefu. Jian'an poetry, Six Dynasties poetry, and Tang Dynasty poetry tend towards a poetic metre based on fixed-length lines of five, seven, (or, more rarely six) characters/verbal units tended to predominate, generally in couplet/quatrain-based forms, of various total verse lengths. The Song poetry
Poetry used at the close of each subsequent stanza until the final quatrain, which is concluded by the two refrains. The remaining lines of the poem have an a-b alternating rhyme. The villanelle has been used regularly in the English language since the late 19th century by such poets as Dylan Thomas, W.H. Auden, and Elizabeth Bishop. A limerick is a poem that consists of five lines and is often humorous. Rhythm is very important in limericks for the first, second and fifth lines must have seven to ten syllables. However, the third and fourth lines only need five to seven.