The was a feudal domain of Japan in the Edo period. Located in what is now Mihara City, Hiroshima Prefecture, it encompassed the southern part of Bingo Province. Its headquarter was Mihara Castle (ä¸ÂÃ¥ÂÂå Mihara-jà Â). At its peak, it was rated at 30,000 koku. For more than two hundred years the daimyà  of Mihara were a collateral branch of the Asano clan who held Hiroshima Domain. It was a subordinate of Hiroshima Domain where the main line of the Asano clan ruled from.
Mihara Castle was built 1567 by Kobayakawa Takakage, the third son of the famous warlord Mà Âri Motonari who controlled most of Aki and Bingo Provinces. It was a large scale castle with 3 baileys, 32 sumi yagura (corner towers), and 14 mon (gates). It was built on the coast and connected two islands giving rise to the nickname Ukishirà  or "floating castle." Kobayakawa Takakage moved from Niitakayama Castle (æ°é«Âå±±åÂÂ), a typical mountaintop castle, to this site to better manage the Mà Âri clan's naval forces and to help protect from Oda Nobunaga who was advancing from the east.
Kobayakawa Takakage took part in the Japanese invasions of Korea (1592âÂÂ98) and adopted Kobayakawa Hideaki who was the adopted son of Toyotomi Hideyoshi. After the Battle of Sekigahara in 1600, Hideaki who had helped Tokugawa Ieyasu gain control of the country was awarded with the defeated Ukita clan's former fiefdoms of Bizen and Mimasaka, for a total of 550,000 koku.
The shà Âgun, Tokugawa Ieyasu, transferred Fukushima Masanori who was formerly the ruler of Kiyosu Castle to Hiroshima Castle of the Hiroshima Domain and his adopted son Fukushima Masayuki became lord of the Mihara Domain from Mihara Castle. Shortly afterwards the Fukushima clan lost favor with the shà Âgun when Fukushima Masanori made repairs to Hiroshima Castle which was prohibited by law. This resulted in the Fukushima clan being replaced by the Asano clan who would rule the domains of Hiroshima, Mihara, Yoshida and Ako until the Meiji Restoration.
The tenshu foundation of Mihara Castle was the largest ever built, similar in size to that of Edo Castle, but the main keep was never actually built. The castle escaped demolition during the Meiji period so that it could be used as Imperial naval base. It was later decommissioned and Mihara Train Station was built on the site in 1894. At this time all the buildings were destroyed and much of the stone walls torn down. The honmaru was further cut to make way for the bullet train in 1975. Together with Kobayakawa's Niitakayama Castle (æ°é«Âå±±åÂÂ) it is designated a National Historic Site.