TOKYO >> The Inuyama Castle keep in Aichi Prefecture, a designated national treasure, has been verified as the oldest keep in Japan.

According to the Inuyama board of education, researchers have confirmed that the keep (the innermost, most prominent structure of the castle) was constructed between 1585 and 1590, after the Battle of Komaki-Nagakute in 1584 and during the reign of Oda Nobukatsu, the second son of warlord Oda Nobunaga.

The date of construction was established by measuring the rings in wooden materials used to build the keep.

Though the Inuyama keep displayed the oldest style among 12 surviving keeps in Japan, earlier documents claimed it was constructed after the Battle of Sekigahara in 1600. But the latest measurements provide scientific evidence of its age.

Those measurements were made by Kazuyoshi Fumoto, a professor of architectural history at the Nagoya Institute of Technology, and Takumi Mitsu- tani from the Nara National Research Institute for Cultural Properties.

An examination of 39 components, including pillars and beams, found that a pillar was made from a tree harvested in 1585, and a floor beam, from a tree in 1588. Wood in other parts of the structure appear to have been harvested during the Tensho period (1573-92).