During the Siege of Osaka, the famous military campaign conducted in the seventeenth century by Japanese warlord Sanada Nobushige, a fortress named Sanada Maru played a key strategic role. But until now, Sanada Nobushige was known to scholars only in historical accounts. Its remains may have been discovered during a recent archaeological excavation.
The ruins were uncovered by the Sanada Maru Excavation Promotion Council during a dig in the Tennoji Ward of Osaka’s Esahi-machi district. The Council encountered a layer of artificially-filled sediment while digging. This leads them to believe that the fortress was larger than researchers thought.
Sanada Maru is said to have branched off of the south side of Osaka Castle’s moat. Osaka Castle was constructed by the Toyotomi clan, allies of Sanada Nobushige. Noboshige, also called Sanada Yukimura, helped the Toyotomi defend their castle against Shogun Tokugawa from 1614 to 1615.
A professor of archaeology at Nara University, named Yohihiro Senda, has challenged the reigning opinion that Sanada Maru was built in a semicircle. Senda, leader of the research group that found the ruins, believes that the fortress may have been square. He draws his conclusions from historical drawings, topographic charts of the area and aerial photographs.
The manmade soil layer was found when the Council excavated seventy square meters of ground near what looked like the moat’s remains.
When Sanada Maru was destroyed, the land surrounding it was probably not changed much. The fill layer, found above what would have been the natural ground level, allows the researchers to estimate the fortress’s shape and size.
Some of the site is now occupied by the Osaka Meisei Gakuen school. But enough remains of the soil layer to suggest that Sanada Maru was rectangular. Its walls were likely about 300 meters from east-to-west and 350 meters from north-to-south.
Yohihiro Senda will present, along with his research team, the entirety of the findings by spring of 2017 in a public session. The discovery coincides serendipitously with the NHK’s historical drama TV programming focusing on the Siege of Osaka.
Senda was an assistant professor at the National Museum of Japanese History and then an associate professor at Nara University in 2005. He was promoted to full professorship in 2009 and also worked as a guest professor at the University of Tubingen and Frankfurt University. From 2014 through 2016, he was president of Nara University. He won the 28th Hamada Seiryo Prize for his work in archaeological study of Japanese castles.