Mōri Terumoto lost his holdings around Hiroshima and was moved to Hagi following the Battle of Sekigahara when he supported the losing side. He built Hagi Castle in 1604, and his family continued to rule over the Chōshū Domain until the Meiji Restoration. The castle was unusual as it was constructed mainly at the base of Mount Shizuki, though a few defences are located on the mountain.
In 1874, much of the castle was destroyed, leaving little but ruins.
The castle is a National Historic site. The castle was registered as a UNESCO World Heritage Site on July 5, 2015 as part of the Sites of Japan’s Meiji Industrial Revolution: Iron and Steel, Shipbuilding and Coal Mining. It is registered as part of Hagi's Castle Town. 
- Schmorleitz, Morton S. (1974). Castles in Japan. Tokyo: Charles E. Tuttle Co. pp. 142–144. ISBN 0-8048-1102-4.
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