Sanada Maru, Fortification structure at Osaka Castle, Japan
Sanada Maru was a small earthen fort attached to the southeast side of Osaka Castle, built with mounded earth and wooden fortifications equipped with firing platforms for cannons and muskets. The structure contained gates, moats, and wooden barriers that formed a tight defensive enclosure protecting the weakest approach to the main castle.
Sanada Nobushige built this fort in the winter of 1614 to defend the weaker southern side of Osaka Castle as the Tokugawa army advanced on the castle. After weeks of fierce fighting, the structure was destroyed as part of the peace settlement that ended the siege.
The fort's design shows how Japanese warriors of the early 1600s arranged walls and lookout spots to control approaches and protect their position. Visitors can still see how the raised ground shaped the layout, with the enclosed space facing toward the main castle grounds.
The site sits on a slight rise near Myojo Gakuen school and once offered clear views across the surrounding area. Markers and models at the location show the original layout and explain the defensive methods that were used.
Local stories tell of secret tunnels supposedly connecting the fort to the main castle, though historians doubt such passages ever existed. What defenders actually built were mines beneath the earth walls to counter enemy attacks with underground explosions.
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