Sima Chengzhen (647–735), twelfth patriarch of the Shangqing line, was the most influential Taoist of the Tang. Three emperors summoned him; he advised Ruizong and Xuanzong on ruling by non-action. His Zuowang Lun — the treatise on sitting-forgetting — is a classic of Taoist meditation; his Tiandi Gongfu Tu first mapped the sacred geography of China: ten great caverns, thirty-six small caverns, seventy-two blessed grounds — the pilgrimage map of Taoism to this day.
His influence ran into poetry too: his friendship with Li Bai and his presence at court made the mountain master a permanent figure of the Tang imagination.