Vietnamese literature has a centuries-deep history. The country has a rich tradition of folk literature, based around the typical 6–to-8-verse poetic form named ca dao, which usually focuses on village ancestors and heroes.[175] Written literature has been found dating back to the 10th-century Ngô Dynasty, with notable ancient authors including Nguyễn Trãi,Trần Hưng Đạo, Nguyễn Du and Nguyễn Đình Chiểu. Some literary genres play an important role in theatrical performance, such as hát nói in ca trù.[176] Some poetic unions have also been formed in Vietnam, such as the Tao Đàn. Vietnamese literature has in recent times been influenced by Western styles, with the first literary transformation movement – Thơ Mới – emerging in 1932.[177]