The flattened stones and pointed balls of clay had languished in two Japanese museum collections for decades.
But when Akihiro Iwata encountered them in 2019, the Japanese archaeologist and curator was sure he had made a “groundbreaking discovery”.
He was convinced that he had found ninja throwing stars early on, or shuriken, used by the mysterious secret agents of feudal Japan as throwing weapons.
These flattened stones – some with sharp edges – are believed to be the predecessors of the infamous ninja throwing star. Credit: Akihiro Iwata/ Saitama Prefecture Historical Museum/Saitama City Board of Education
Iwata is expected to publish a book about his findings in March after the 430-year-old weapons were put on display last summer.
All of the artifacts were excavated from archaeological sites in Saitama and Hachioji, a city in the western part of Greater Tokyo, between 1920 and 2010 and held in two museum collections in those cities.
He told CNN that the flat, sharp-edged green stones found in the ruins of Iwatsuki Castle and the Owada jin’ya administrative headquarters in Saitama were likely prototype throwing stars. And the fired clay balls found at Hachioji Castle are likely “makibishi” or caltrops – which can injure the feet of enemy soldiers and horses when put down or thrown on the ground.
“I knew they were ninja weapons because the structure was so similar to weapons found in the Edo period (1603 to 1867),” Iwata said in a phone interview. However, these weapons were made of steel, not stone.
Siege of Odawara
Yamada, who was not directly involved in the research, said he agreed with Iwata’s assessment that the artifacts were prototype ninja stars and caltrops.
“These mercenaries served under feudal lords as spies and scouts who gained information on enemies,” Yamada said.
During the Edo period (1603 to 1867), they continued to work as spies and as keepers of public order in walled towns and acted as bodyguards for important figures, said Yamada, who has noted that most of the ninja weapons discovered were from this time.
Throwing stars used by ninjas of the Edo period (1603 to 1867). Credit: Akihiro Iwata/Kawagoe Historical Museum
Akihiro Iwata found unglazed clay caltrops with spikes. Some lacked spikes, suggesting they were hastily made or did not take the intended shape. Credit: Akihiro Iwata/ Saitama Prefecture Historical Museum/ Hachioji City Board of Education
Four unglazed clay balls were among the artifacts discovered in the ruins of Hachioji Castle around 1960, Iwata said. Each ball, measuring about 1–3 cm (0.4–1.2 inches) in diameter, has four pointed protrusions.
Iwata explained that the artifacts were likely the weapons of a group of low-ranking warriors who swung into action as ninja to defend the castle against the enemy attack at Hachioji. Some were probably hastily made because they look flawed, he added.
“They threw rocks and shuriken at them to slow down the enemy’s progress and flee,” he said.
But despite their best efforts, the Toyotomi and Tokugawa clans defeated the Hojo clan and captured Iwatsuki and Hachioji castles.
“A lot of things were left behind because the Toyotomi army attacked and burned down the castles after they fell during the Odawara invasion. The items found are proof of the fall of the castles,” Iwata said.
Weapons used by ninjas in the Edo period resemble in shape the rudimentary stone throwing stars identified by Akihiro Iwata. Credit: Akihiro Iwata/Kawagoe Historical Museum
Iwata said his sightings were likely just the tip of the iceberg, with many other undocumented ninja artifacts hidden away in museum collections.
“It made me think there was a whole treasure trove of ninja weapons out there waiting to be discovered,” Iwata said.
Top image caption: Flattened stones discovered in the ruins of a castle in Saitama are said to be the precursors to the ninja throwing star.