Kigo was the Rokugani term for “seasonal word” in poetry forms, which related the poem to one of the four seasons. The incorporation of subtlety in the kigo was often praised. As a token of respect to the Emerald Throne, most haiku collections published before the 12th century based their kigo on the seasons as they were perceived at Otosan Uchi, the Imperial City. Books containing standardized kigo were commonly sold there until the city fell in 1159.