Production of Puerh can be traced back to the Tang Dynasty (618-907). The exotic offering was first written about in the ancient treatise, "Book on Barbarians" published after a visit to ancient Yunnan province by a Tang government official. (Evidently the Imperialists didn't think too highly of the province's early inhabitants.)
In it he writes, "The tea is yielded from the mountains beyond Yinsheng City and picked from scattered trees without processing. Barbarians of Mangshe drink tea by cooking it with pepper, ginger and cassia." While this form of Puerh was certainly different from the Puerh cakes more commonly known in today's world, archaeological records indicate that the same style of specialized leaf fermentation was being implemented, so the classification fits.