Hiroshima Castle (広島城, Hiroshimajō), also called the Carp Castle, is a good example of a castle built on a plain in the center of a city as opposed to hilltop and mountaintop castles. Its main keep is five stories tall, and its grounds are surrounded by a moat. Also within the castle's precincts are a shrine, some ruins and a few reconstructed buildings of the Ninomaru (second circle of defence).
Hiroshima developed as a castle town, whereby the castle was both the physical and economical center of the city. Built in 1589 by the powerful feudal lord Mori Terumoto, Hiroshima Castle was an important seat of power in Western Japan. While it was spared the demolishment that many other castles met during the Meiji Restoration, like the rest of the city, Hiroshima Castle was destroyed by the atomic bomb in 1945. https://www.japan-guide.com/e/e3402.html