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
Classic of Poetry for much of Chinese history. One of the characteristics of the poems in the "Classic of Poetry" is that they tend to possess "elements of repetition and variation". This results in an "alteration of similarities and differences in the formal structure: in successive stanzas, some lines and phrases are repeated verbatim, while others vary from stanza to stanza". Characteristically, the parallel or syntactically matched lines within a specific poem share the same, identical words (or characters) to a large degree, as opposed to confining the parallelism between lines to using grammatical category matching of the words in one line with