Gassan, at only 184 meters above sea level is not particularly high, but its shape makes it an obvious choice for a castle, so its not surprising that there was one here for about 1,000 years.
Gassan Toda castle is classified as one of the top 100 castles in Japan, and one of the top 3 mountain castles of the Sengoku period. It is most strongly associated with the Amago Clan who ruled over a large territory
Gradually the Amago lost ground to the Mori Clan, until eventually the Amago made their last stand here.
The castle withstood a first siege, but fell during a second siege, and if I remember correctly it was due to treachery by one of the Amago vassals. It seems that an awful lot of battles were won by vassals switching sides. So much for bushido and loyalty, treachery seems to be the norm.
In 1600 Ieyasu gave the domain to Yoshiharu Horio, but he decided to move his headquarters to what is now Matsue so he dismantled Gassan Toda and used it in the construction of Matsue Castle.
Since the last time I was here they have built a couple of small reconstructed buildings, including one right on top of the mountain where the keep once stood. Last time I slept out here I slept on a bench. Now I have a roof.