Aikō

Aikō occupied the middle of Sagami Province, from the Sagami River and Tanzawa Mountains northward toward Musashi. River plains, hills and mountain approaches created distinct farming and forest zones. Roads through the valleys connected coastal Sagami with the Kantō interior and the roads leading toward Edo.

During the Heian through Sengoku periods, the land formed part of a vast shōen held by the Ōe clan and their descendants, the Mōri of Chōshū. Distant proprietors claimed rice dues and labor from local cultivators while estate managers organized fields, water and villages. The Hōjō of Odawara and Takeda of Kai later contested the district during their struggle for eastern Japan.

Under the Tokugawa shogunate, authority became more fragmented. The area was nominally part of Odawara Domain, but much belonged to tenryō lands administered from Edo through hatamoto. After 1706 a branch of the Ōkubo clan established Ogino-Yamanaka Domain in part of the district, while other portions belonged to Karasuyama Domain. River and mountain boundaries thus supported overlapping estates, domains and direct shogunal holdings rather than one continuous town history. Local villages maintained irrigation, woodland and upland paths. Estate boundaries followed ridges and streams, and disputes over water reveal how local managers negotiated between villages and distant proprietors. Rice, millet and timber moved along valley roads toward markets near the Sagami River. Estate records linked rice dues with local festivals and irrigation duties.