Also kanshi 干支 and eto えと. Ch: shigan shierzhi. Lit. ten stems and twelve branches. Referred to as the Chinese zodiacal symbols or sexagenary cycle. The system, invented no later than the Yin dynasty and adopted by the Japanese, probably in the early 7th century, was used to indicate the cardinal directions and as a way of counting years, months, days, and hours as well as a geomantic system for telling fortunes. The ten stems or trunks jikkan 十干 are ; kō 甲, otsu 乙, hei 丙, tei 丁, bo 戊, ki 己, kō 庚, shin 辛, jin 壬, and ki 癸. The ten stems were given alternate names (readings) based on the combination of the five elements which are in turn based on the idea of yin (Jp: in 陰) and yang (Jp: yō 陽). The yang "e" 兄 (elder) or yin "to" 弟 (younger) were joined with ki 木 (wood) to form ki no e 甲 and ki no to 乙, with hi 火 (fire) to form hi no e 丙 and hi no to 丁, with tsuchi 土 (earth) to form tsuchi no e 戊 and tsuchi no to 己, with kane 金 (metal) to form kano e 庚 and kano to 辛, and with mizu 水 (water) to form mizu no e 壬 and mizu no to 癸. The twelve branches jūnishi 十二支 are: shi or ne 子 (rat), chū or ushi 丑 (ox), in or tora 寅 (tiger), bō or u 卯 (hare or rabbit), shin or tatsu 辰 (dragon), shi or mi 巳 (snake), go or uma 午 (horse), mi or hitsuji 未 (ram or sheep), shin or saru 申 (monkey), yū or tori 酉 (rooster), jutsu or inu 戌 (dog), and gai or i 亥 (boar). Like the Chinese, the Japanese held that one's personality was determined by the animal of one's birth year. In Edo period painting, the twelve animals were depicted either separately or collectively and, on occasion, with humans imitating the animal's appearance. Conversely, the zodiac animals could serve to parody human activities such as poetry contests.
The ten stems and twelve branches were combined in two-symbol units to form a cycle of sixty which was repeated ad infinitum for counting years. Alternate names (readings) for the 60 units are formed by combining the twelve animal names with those ten stems derived from the five elements joined with e or to. For example, 甲子 reads either kōshi (also kasshi) or ki no e ne.
This system is important in art history for dating art works. For example, according to the inscription on the back of the halo *kōhai 光背, the bronze statues of *Shaka 釈迦 with an attendant in Hōryūji Daihōzōden 法隆寺大宝蔵殿 were made "in the year of boshi 戊子 for Minister Soga 蘇我." Since the statues are in the very early Asuka period style and the Soga clan flourished until mid-7th century, "the year of boshi" can be pinpointed to 628.