THE FIVE PHASES · LESSON 2 OF 7 · 12 MIN
The Stems and the Branches
The ten heavenly stems and twelve earthly branches, the sixty-day cycle written on the Shang oracle bones and never broken since, and the twelve animals.
Long before it named years, China counted days in a cycle of sixty. Almost every Shang oracle bone, the cracked ox shoulder-blades and turtle shells of the late second millennium BCE, opens with a date in it. The count has run unbroken since at least the 8th century BCE — eclipses recorded in the Spring and Autumn Annals prove it — and it is still running today.