Ancient poetry is a general term for ancient Han poetry. From the perspective of meter, ancient poetry can be divided into ancient poetry and modern poetry. Taking the Tang Dynasty as the boundary, poetry in the past was all ancient poetry. After that, ancient poetry gradually declined and died out. Four-character ancient poetry refers to ancient poetry.
All ancient poems are classified according to the number of words in the verses. Four characters and one sentence are called four-character ancient poems, or Sigu for short. "Siyan" refers to a poem composed of four characters. Four-character poems refer to poems written generally or basically in four-character sentences.
Four-character ancient poems have been used by people as far back as the era of The Book of Songs. The "Guofeng", "Xiaoya", and "Daya" in the "Book of Songs" all use four-character poetry as the basic genre. But it gradually declined in the Tang Dynasty, and few people wrote about it.