Kaya

Kaya was a district of Bitchū whose Ashimori River country became a battlefield in 1582. Hashiba Hideyoshi, advancing against the Mōri for Oda Nobunaga, sent Ukita troops into Ashimori in early spring. Nearby Takamatsu Castle formed part of a chain of seven frontier strongholds. Its lord Shimizu Muneharu rejected Hideyoshi's offer to change sides, trusting both Mōri support and the marshland surrounding his position.

After taking neighbouring castles, Hideyoshi encircled Takamatsu. Rather than continue costly assaults, he built an embankment and diverted water from the Ashimori River; another channel brought water from the Naruya. The siege turned the low-lying agricultural landscape into a weapon. Field fortifications on the surrounding hills supported the advance, tying the district's roads, ridges and waterways directly to the struggle between the Mōri and the forces unifying Japan.