In natural languages, expressions with spatial meaning often evolve into expressions with temporal meaning. The Chinese language is no exception. It possesses horizontal time expressions (like “front” and “back”), as well as vertical time expressions (like “up” and “down”). This article attempts to show that vertical expressions such as “in previous eras”, “in ancient times”, “the first ten days”, etc. were attested in pre-Qin documents. Vertical expressions like “shangwu” (above-noon) and “xiawu”(below-noon) were triggered by the word “wu” used to express an Earthly Branch, and began to spread with words like “zhongwu” (noon) in the Tang and Song dynasties. Vertical words expressing the “past” actually did exist in Old Chinese, but the system seems to have formed relatively late. In the Ming and Qing dynasties, the vertical expression system in Chinese truly matured. Some of these expressions could be found in Qing Dynasty literature, but have been abandoned in modern Chinese. Today many Chinese dialects retain two systems (horizontal and vertical) of time expression.