 The oldest documented use of the word "Tennō" is on a wooden slat, or "mokkan", that was unearthed in Asuka-mura, Nara Prefecture in 1998 and dated back to the reign of Emperor Tenmu and Empress Jitō.Throughout history, Japanese Emperors and noblemen appointed the position of chief wife, rather than just keeping a harem or an assortment of female attendants.The Japanese imperial dynasty consistently practiced official polygamy, a practice that only ended in the Taishō period (1912–1926).