一条天皇
The Japanese imperial dynasty consistently practiced official polygamy until the Taishō period (1912–1926). Besides his empress, the emperor could take, and nearly always took, several secondary consorts ("concubines") of various hierarchical degrees. Concubines were allowed also to other dynasts (Shinnōke, Ōke). After a decree by Emperor Ichijō (), some emperors even had two empresses simultaneously (identified by the separate titles "kōgō" and "chūgū"). With the help of all this polygamy, the imperial clan could produce more offspring. (Sons by secondary consorts were usually recognized as imperial princes, too, and such a son could be recognized as heir to the throne if the empress did not give birth to an heir.)