Premise: Hayashi castle was a 15th-century castle, (alternatively known as Hayashi-jo, Fukuyama-jo) in Satoyamabe village, Matsumoto city, Nagano, Japan. A mountain-type castle, it is now largely in ruins. The site is sometimes regarded as one castle, or two castles, Hayashikojo (the small castle) and Hayashiohjo (the larger castle).
Hypothesis: A castle was built during the 1400's in the Nagano region.