The Jo clan was a powerful gozoku (local clan) siding with the Heike (the Taira clan), but the Jisho-Juei War (which conflict is commonly known as the Genpei War, battles of which taking place during the Jisho and Juei eras) brought about the ruin of this clan, thus being obliged to go into hiding.
城氏は有力な平家方の豪族であったが、治承・寿永の乱を経て没落、一族は潜伏を余儀なくされる。