A defense mechanism often integrated in the Japanese castles design was the stone drop window, ishi-otoshi in Japanese.

At the corners of the yagura turrets in this photo from the Kumamoto castle, you can see a wooden structure extended outside, with an opening on the bottom. The ishi-otoshi was made large enough to allow throwing large rocks, but narrow enough to prevent a man from crawling through it.

Kumamoto Castle, Kumamoto

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Yesterday’s Japan Photo: Phoenix Hall, Uji, Kyoto