Shen Yue 沈約 (441–513) is widely believed to have created the poetic metrical theory of si sheng ba bing 四聲八病 (four tones and eight defects) and divided the four tones into ping 平 (level tone) and ze 仄 (oblique tone) categories, thus forming the binary contrast prosodic system in Chinese regulated-style verse. Victor Mair and Tsu-lin Mei have further argued that the rules of the “eight defects” and the concept of ping-ze contrast were designed by Shen Yue under the influence of Sanskrit prosodic theory. The most challenging puzzle that remains for scholars in the field is to understand why Shen Yue and the other Six dynasties poets failed to follow their own prosodic theory in their composition practices. The rise of regulated-style verse in the history of Chinese literature still remains something of a mystery. Through a case study of Shen Yue's poems, this essay aims to solve the puzzle by exploring: (1) the nature of poetic prosody, (2) tonal prosodic patterns in Chinese regulated verse, (3) problems with the Sanskrit origins hypothesis of Chinese tonal prosody, and (4) the pathways of Chinese poetic metricalization from the Six dynasties (222–589) to the Tang dynasty (618–907).