Hiroshima Castle, located in Motomachi, Naka Ward, Hiroshima City, Hiroshima Prefecture, is one of the most important flatland castles from the Azuchi–Momoyama period to the Edo period, and is now designated as a National Historic Site. Built by Mōri Terumoto on the delta at the mouth of the Ōta River, it is regarded—alongside Osaka Castle and Okayama Castle—as a representative example of early modern Japanese castles, and together with Nagoya Castle and Okayama Castle, it is counted among the “Three Great Flatland Castles of Japan.”
In the early Edo period, Fukushima Masanori expanded the castle grounds, at one point extending the outer moat to cover about 900,000 square meters. Thereafter, it served as the seat of the Hiroshima Domain’s Asano clan for twelve generations, ruling over a domain assessed at 426,000 koku. Records from the mid-Edo period indicate that the castle featured a grand keep complex with a five-story main keep and three-story secondary keeps, as well as 88 turrets, reflecting its impressive scale. The original main keep, completed in 1592, was noted for its lower walls with exposed wooden planks and the balcony on its top floor, earning designation as a National Treasure in 1931. However, the atomic bombing of Hiroshima in 1945 destroyed the keep and most of the castle structures.
The current main keep was reconstructed in 1958 and now serves as the Hiroshima Castle History Museum. The preserved areas mainly include the ruins of the honmaru (main bailey) and ninomaru (second bailey). Outside the designated historic site, remnants of stone walls and earthen embankments can still be seen.
Hiroshima Castle is also known by the nickname “Carp Castle” (Rijō). One theory attributes the name to the old place name “Ko’iura” (“Koi” being an archaic term for carp), while another suggests it comes from the abundance of carp in the castle moats or from the keep’s dark exterior appearance. The nickname appears in literature from the late Edo period and has since influenced modern place names and facilities such as “Rijō-dōri” (Carp Castle Street) and “Rijō Kaikan,” as well as inspiring the name of the Hiroshima Toyo Carp professional baseball team.
