- Ryuzoji Takanobu, Nabehima Naoshige (5,000?) vs. Ôtomo Chikasada (60,000)
- Date: 1570
- Location: Hizen province
- KIA: Ôtomo Chikasada
The Ôtomo of Bungo province and the Ryûzôji of Hizen Province were long-time rivals and by 1570 were the most powerful clans in northern Kyushu. In 1570, Ôtomo Sorin assembled a massive army, intent on crushing his enemy Ryûzôji Takanobu, the 'Bear of Hizen'. History records this host as numbering some 60,000 men and including most of the Ôtomo's allied families. These included the Arima, Imayama, Oda, Usuki, Kumashiro, and Hetsugi. Although this figure seems excessive, the Ôtomo's lands were relatively populous and they were to prove capable of fielding quite a large force on other occasions, notably for the campaign against the Shimazu that culminated in the Battle of Mimigawa (1578). Sorin placed his army under the command of his younger brother, Ôtomo Chikasada, a veteran of earlier campaigns into Hizen, Chikugo, and elsewhere. Learning of the Ôtomo's advance, Ryûzôji Takanobu hastily led a small force to Saga castle, which was in the hands of his capable retainer, Nabehima Naoshige. Here Takanobu and Naoshige were surrounded by the Ôtomo, who arrayed their forces in a crescent around Saga, hemming the Ryûzôji men in, with the sea to the south acting to complete the ring. Chikasada planted his standard on Iyama, somewhat to the northwest of Saga. Noting the large disparity in numbers, Chikasada conducted a rather casual siege, intending to storm the fort in due course. However, Nabeshima Naoshige noted that the Ôtomo army's discipline was lax and their forces poorly deployed to counter a surprise attack, which he suggested to Takanobu in council. Although hesitant, Takanobu agreed to condone an attack, trusting Nabeshima's knowledge of the ground, and, under cover of darkness, Naoshige led him men out of the castle and made their way around Iyama. In a violent charge, they drove into Chikasada's headquarters and Chikasada himself was slain by the Ryûzôji warrior, Narimatsu Nobukatsu. The Ôtomo army fell into chaos and withdrew. Although rarely mentioned in English works on the period, Iyama represents one of the great surprise attacks of the 16th Century, akin to Okehazama (1560) and Kawagoe (1545) and certainly demonstrates the importance of morale and central leadership in the outcome of Sengoku battles.