From Castles in Japan, by Morton S. Schmorleitz (Tuttle, 2011), Kindle Loc. ~1850ff:
In 1589 Mori Terumoto began what would be an eight-year project: he built a castle on an island in the delta of the Ota River, calling this part of his domain "Hiroshima," which means "wide island." At the beginning of the 17th century, the Mori fief was given to the Asano Clan, who held the castle until 1871. During the Restoration all of the buildings were torn down except the keep.
The castle is noted for the fact that the Emperor Meiji resided there for seven months during the war with China (1894-95). When Japan became involved in the war of 1904-5 with Russia, the castle was used as a troop garrison.
At 8:15 on the morning of August 6, 1945, Hiroshima Castle, along with a large portion of the city, was completely demolished in the historic first atomic attack. Reconstruction of the castle donjon was begun in 1958. It is built on the original foundation and is an exact replica of the former keep in exterior appearance. The structure is five stories, 117 feet high, and is in the style of the early Momoyama period. The donjon houses a museum and a lookout.