This sort of organization was established by such clans as the Satake clan, Utsunomiya clan and Oda clan, and the words '当洞' (todo) or 'OO 洞中' (OO dochu) were used in the documents and letters of diplomatic negotiations exchanged between daimyo (Although the daimyo of the Mori clan, who was the daimyo of the western region of Japan, had a similar organization and also used the character '洞' in their documents, it is considered to be an exceptional case).
こうした形態は結城氏や佐竹氏、宇都宮氏、小田氏などに見られ、これらの大名間の外交交渉の文書・書簡を見ても「当洞」・「○○洞中」などの表現が見られる（なお、西国でも似たような構造を有した毛利氏の文書中にも「洞」の語が登場するが、特異な例と考えられている）。