Letter from Sengoku period warlord Nobunaga authenticated, tracing advance into western Japan

Courtesy of the Taigan Historical Museum
A letter from Nobunaga to Hideyoshi in a collection from the Taigan Historical Museum in Machida, Tokyo.

A letter from the famous feudal warlord Oda Nobunaga (1534-1582) to warlord Hashiba Hideyoshi (1537-1598), later known as Toyotomi Hideyoshi, asking him to address disturbing moves by warlord Bessho Nagaharu (unknown-1580) has recently been verified as authentic.

Nobunaga sent the letter after he had dispatched Hideyoshi as general-in-chief to “pacify” western Japan. In the letter, Nobunaga asked Hideyoshi to deal with disturbing moves made by Nagaharu, a warlord from Harima Province (in what is now southwestern Hyogo Prefecture), who later disobeyed Nobunaga and killed himself.

The letter is a valuable historical document that traces events that occurred in the course of Nobunaga’s advance into western Japan.

Dated March 13, the letter is believed to have been sent to Hideyoshi after his arrival in Harima Province on Feb. 23, 1578. The Taiyo Collection Foundation, an organization that collects historical documents from the Sengoku warring states period in the 15th and 16th centuries, obtained the letter.

Hiraku Kaneko, an associate professor at the Historiographical Institute of the University of Tokyo and an expert in Nobunaga studies, recently verified the letter as authentic based on its content, including the black seal of Nobunaga, which reads “Tenka fubu,” as well as the handwriting of the warlord’s secretary, which is similar to that seen in Nobunaga’s letters from the same period.

Nobunaga started the letter by saying he had learned that there was trouble between Hideyoshi and Nagaharu. Nobunaga then described Nagaharu as a man who has always been loyal to him and told Hideyoshi to address the trouble and report back to him on how it went.

However, in an existing document sent to Kuroda Kanbei that is dated March 22 of the same year, asking Kanbei to cooperate with Hideyoshi to defeat Nagaharu, Nobunaga described him as an enemy.

“Hideyoshi began his two-year siege of Miki Castle [in current Hyogo Prefecture] in late March. This letter with Nobunaga’s black seal was issued just before that moment,” said Ryosuke Nakamura, curator at the Taigan Historical Museum in Machida, Tokyo, which exhibits historical documents from the Taiyo Collection.

“[The letter] shows Nobunaga trying to resolve the situation peacefully at the stage [when the letter was written],” Nakamura, an expert in Japanese medieval history, added.

Only a few original documents sent from Nobunaga to Hideyoshi are known to exist, including those that remain with the Hosokawa and Kuroda families and other feudal lords who served Nobunaga or Hideyoshi, according to Kaneko.

“Even though he had heard of trouble between Hideyoshi and [Nagaharu], Nobunaga had praised Nagaharu as a loyal and faithful man. The letter is an important historical document that shows Nobunaga changing his mind, leading to the defeat of Nagaharu,” said Kaneko.

The letter is on display for the first time at a special exhibition featuring the collections of the Taigan Historical Museum held at the Fujieda City Folk Museum and Literature Museum through Dec. 18.