丸岩城, Mountain fortress in Nagano Prefecture, Japan
Maruyama Castle is a mountain fortress in Nagano Prefecture built on a hilltop with natural slopes. The site features preserved stone walls, water-filled ditches, and multiple gates that divided different sections of the layout.
The fortress was built during the Sengoku period to control the mountain region as a military outpost. It was eventually abandoned before the larger castle architecture trends of that era transformed the landscape.
The site shows how warriors designed spaces to control movement and slow down invaders through clever layout. Walking through the narrow passages today, you can sense how these small entrances forced attackers to move carefully and lose their advantage.
The site is accessed through marked trails that lead to main areas where foundation stones and defensive trenches remain visible. Visitors should expect uneven ground and steep sections that require sturdy footwear.
The fortress has multiple small entrances designed to force attackers into narrow, winding passages that slowed their advance. This clever design feature was typical of military thinking at the time, neutralizing any advantage an invading force might gain.
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