Raizan Castle, Ancient mountain fortress in Itoshima, Japan.
Raizan Castle is an ancient mountain fortress in Itoshima featuring two kilometers of earthen ramparts arranged across steep slopes. The site contains eight watchtower positions that controlled different approaches to the stronghold.
Construction began in 756 after Kibi no Makibi returned from the Tang court with advanced fortification knowledge. The fortress represented military innovation learned through his diplomatic service in China.
The site reflects craft skills from the Nara period through its foundation stones and roof tiles still visible today. Visitors can observe how builders organized their work across the different levels of the fortress.
The site is open for visitors to explore the earthen ramparts and watchtower locations up close across the hillside. The nearby Itokoku History Museum displays excavated artifacts and provides additional context about the fortress.
The fortress builders mixed seawater and lime-based materials into the earthwork to strengthen the fortification walls against weathering. This technique reveals how workers understood durability in a humid mountain environment.
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