the ten 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 number like Roman I, II, III)