Château de Kasugajo, Mountain castle in Joetsu, Japan.
Kasugajo is a mountain fortress in the Joetsu region built on two ridges at roughly 180 meters elevation. The complex features earthen ramparts and dry moats positioned across multiple stepped terraces on the slopes.
The fortress was built by the Nagao clan and became the main stronghold of warlord Uesugi Kenshin in 1548 during the Sengoku period. It served as a military center during an era of intense regional power struggles.
The fortress is recognized among Japan's most important mountain castles, holding special status in the country's military heritage. It represents a specific approach to fortification that defined an era of regional warfare.
The walk to the ruins takes about 20 minutes from Kasugayama Shrine and passes through natural terrain. The site offers views of Joetsu city and the Sea of Japan from higher points along the route.
The fortress was built without stone walls and relied instead on earthen defenses and strategic positioning on the terrain. This construction method shows a different approach to fortification compared to later castle designs using stone.
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