the 10 heavenly stems 甲 jiǎ, 乙 yǐ, 丙 bǐng, 丁 dīng, 戊 wù, 己 jǐ, 庚 gēng, 辛 xīn, 壬 rén, 癸 guǐ (used cyclically in the calendar and as ordinal numbers like Roman I, II, III)

十干与十二支相配合，形成了中国传统的干支纪年法。