지쿠젠 국
After the defeat of the Ryūzōji clan at the Battle of Okitanawate in 1584, Shimazu Yoshihisa refocused his attentions on the Ōtomo clan and a campaign was started against their dominions. The siege of Iwaya Castle resulted after the Shimazu invasion of Chikuzen Province. The castellan of Iwaya was Takahashi Shigetane, one of the most trusted retainers of the Ōtomo, and held the fortress with a small garrison of around 763 soldiers. When the invading army of around 20,000 soldiers put the castle under siege the situation seemed untenable, but the castle managed to hold for two weeks.