Han poetry as a style of poetry resulted in significant poems which are still preserved today, and which have their origin associated with the Han dynasty era of China, 206 BC – 220 AD, including the Wang Mang interregnum (9–23 AD). The final years at the end of the Han era (known by the name Jian'an, 196—220) often receive special handling for purposes of literary analysis because, among other things, the poetry and culture of this period is less than typical of the Han period, and has important characteristics of its own, or it shares literary aspects with the subsequent Three Kingdoms period. This poetry reflects one of the poetry world's more important flowerings, as well as being a special period in Classical Chinese poetry, particularly in regard to the development of the quasipoetic fu; the activities of the Music Bureau in connection with the collection of popular ballads and the resultant development of what would eventually become known as the yuefu, or as the rhapsodic formal style; and, finally, towards the end of the Han Dynasty, the development of a new style of shi poetry, as the later development of the yuehfu into regular, fixed-line length forms makes it difficult to distinguish in form from the shi form of poetic verse, and at what point specific poems are classified as one or the other is somewhat arbitrary. Another important poetic contribution from the Han era is the compilation of the Chuci anthology, which contains some of the oldest and most important poetic verses to be preserved from ancient China, as well as the transmission of the Shijing anthology.