Battle of Miyajima The 1555 was the only battle to be fought on the sacred island of Miyajima ; the entire island is considered to be a Shinto shrine , and no birth or death is allowed on the island . Extensive purification rituals took place after the battle , to cleanse the shrine and the island of the pollution of death . The Battle of Miyajima was the turning point in a campaign for control of the Ōuchi clan and of Aki Province , a strategically important province for establishing control of western Honshu . It was an important step for the Mōri clan in taking the foremost position in western Japan , and cemented the reputation of Mōri Motonari as a cunning strategist . Background . In 1551 , Sue Harukata revolted against his lord Ōuchi Yoshitaka , forcing him to commit seppuku . Sue installed the next lord of the clan , Ōuchi Yoshinaga , but effectively led the Ōuchi family and its armies , intent on military expansion . In 1554 , Mōri Motonari , as a vassal of the Ōuchi clan , wanted to avenge the betrayed Yoshitaka , and so he rebelled against Sue , whose territorial ambitions were depleting clan resources . The heavily outnumbered force under Mōri attacked and defeated Sue at the Battle of Oshikibata . Mōri then departed from the mainland to build a fort , known as Miyao Castle , on Miyajima while proclaiming publicly his woe that it would not hold out long against an attack . The battle . Miyao Castle was built on a hill near Itsukushima Shrine and facing the mainland , making it a visible and tempting target . Sue commandeered a fleet of merchant vessels and prepared the troops of the Ōuchi clan to cross the channel . In the early hours of 15 October , Sue attacked Miyao Castle in an amphibious frontal assault . Meanwhile , Mōri took advantage of his absence to seize Sakurao Castle , Sue ' s castle on the mainland . With an embarkation point secured , Mōri Motonari continued with his elaborate plan . He had enlisted the aid of local pirates who agreed to transport his troops to Miyajima . The fleet carrying the Mōri forces set out in a driving thunderstorm . Their approach thus obscured , Motonari and two of his sons , Kikkawa Motoharu and Mōri Takamoto , landed on the east side of the island , to the rear of the Sue force . Meanwhile , Motonari ' s third son , Kobayakawa Takakage , sailed straight toward Miyao Castle in a feint , then retreated so he could be in a position to return the following day , his attack synchronized with the overland assault . At dawn , Takakage and his 1 , 500 troops landed before the small fortress , and the sound of shell trumpets signalled that all units were in position and the attack commenced . As Takakage ' s force rushed the front gate of Miyao Castle , Mōri and his troops hit the Ōuchi position from behind . Caught completely by surprise , many of the Ōuchi troops scattered in disarray . Hundreds tried to swim to the mainland and drowned in the attempt . Many more saw that defeat was inevitable and committed " seppuku " . By 18 October 1555 , resistance had ended at a cost of about 4 , 700 dead among the Ōuchi army . Sue Harukata escaped from the confines of Miyao Castle , but when he saw that escape from the island was not possible , he also committed suicide by " seppuku " . Aftermath . Immediately after the battle , Mōri Motonari ordered that the bodies of the fallen troops be removed to the mainland , and then ordered that the entire battlefield be cleansed of the blood that was spilled , to the point that buildings were scrubbed , and blood - soaked soil was removed from the island . The Mōri clan later funded several construction or renovation projects on the island . The remains of Sue Harukata were transported back to the mainland and positively identified at Sakurao Castle before being accorded a funeral and burial in the cemetery of a nearby Buddhist temple in present - day Hatsukaichi city , Hiroshima Prefecture . The Sue forces at Miyajima are estimated to have been about 20 , 000 to 30 , 000 men , and though estimates of the combined forces under Mōri Motonari range widely from 4 , 000 to 10 , 000 troops , it is clear that Mōri was heavily outnumbered . This victory brought the Mōri clan into a preeminent position in western Japan , and established their reputation for strategy and naval tactics .