Middle Chinese, the language of many Chinese poets, is tonal. For this reason, tone plays an important role in many Classical poems. In the context of poetry, tones are divided into two groups:
平 (píng) level tones
仄 (zè) oblique tones
平 corresponds to today’s first and fourth tones
仄 corresponds to today’s second and third tones
Likewise, Classical Chinese tones are simply referred to as 平仄 (píngzè).
Many poetic structures rules on how and where level and oblique tones can be used. As such, they are an important part of appreciating and understanding historical Chinese poems.
Unfortunately, we don’t know exactly how Middle Chinese sounded, so the tone marks here are only an educated guess.