During the greater part of China's first great period of unification, begun with the short-lived Qin Dynasty (221 BC – 206 BC) and followed by the centuries-long Han Dynasty (206 BC – 220 AD), the "shi" form of poetry underwent little innovation. But a distinctively descriptive and erudite "fu" form (not the same "fu" character as that used for the bureau of music) developed that has been called "rhyme-prose," a uniquely Han offshoot of Chinese poetry's tradition. Equally noteworthy is Music Bureau poetry ("yuefu"), collected and presumably refined popular lyrics from folk music. The end of the Han witnesses a resurgence of the "shi" poetry, with the anonymous "19 Old Poems". This collection reflects the emergence of a distinctive five-character line that later became "shi" poetry's most common line length. From the Jian'an reign period (196 – 220 AD) onward, the five-character line became a focus for innovations in style and theme. The Cao family, rulers of the Wei Dynasty (220 – 265 AD) during the post-Han Three Kingdoms period, distinguished themselves as poets by writing poems filled with sympathy for the day-to-day struggles of soldiery and the common people. Taoist philosophy became a different, common theme for other poets, and a genre emphasizing true feeling emerged led by Ruan Ji (210–263). The landscape genre of Chinese nature poetry emerged under the brush of Xie Lingyun (385–433), as he innovated distinctively descriptive and complementary couplets composed of five-character lines. A farmland genre was born in obscurity by Tao Qian (365–427) also known as Tao Yuanming as he labored in his fields and then wrote extolling the influence of wine. Toward the close of this period in which many later-developed themes were first experimented with, the Xiao family of the Southern Liang Dynasty (502–557) engaged in highly refined and often denigrated court-style poetry lushly describing sensual delights as well as the description of objects.