SHIZUOKA--The remains of an extravagant castle keep belonging to a powerful warlord have been found under the massive inner tower built by Tokugawa Shogunate founder Tokugawa Ieyasu (1542-1616) at Sunpu Castle Park.

The structure is believed to have been built in the 1590s at the behest of Toyotomi Hideyoshi (1537-1598), only years before the larger building was completed.

The Shizuoka city government said Oct. 16 that the buildings reflected a change in power at the site.

A city government-led excavation project turned up 330 or so shards of roof tiles embellished with gold leaf in June and July.

In August, project members found remnants of a smaller stone foundation spanning 37 meters north-south and 33 meters east-west, partially buried under the southeast corner of the larger foundation. They noted that different masonry techniques were used in the construction.

The size of the base of the later structure spanning about 68 meters north-south and 61 meters east-west was first confirmed in a dig last fiscal year. The base is substantially larger than that of Edo Castle in Tokyo, and the biggest in Japan.

The older base was built with the “nozurazumi” technique, which utilizes naturally found stones, the same method used for Matsumoto, Ueda and Komoro castles, all in modern-day Nagano Prefecture, and is a characteristic of stone walls built when Hideyoshi held power.

It is highly likely that Hideyoshi ordered construction of the luxury castle keep to check Ieyasu, who originally built Sunpu Castle in the 1580s before moving to Edo, today's Tokyo, in 1590.

“We believe that while Hideyoshi displayed his power through the splendor of his castle keep, Ieyasu tried to display his might through the sheer size of the castle keep foundation after taking the castle back,” said a city government official from the history and culture division.

The abundant use of gold-gilt roof tiles is another indication of Hideyoshi's presence. Such tiles adorned a castle-like mansion he ordered built in Kyoto from 1586 to 1587.

Gold-gilt tiles are also known to have graced the castles either under the warlord's direct control or of strategic importance at the time, including Fushimi Castle in Kyoto, Osaka Castle, and Hizen Nagoya Castle in Saga Prefecture.

Ieyasu built Sunpu Castle between 1585 and 1589. After he relocated to Edo in 1590, Nakamura Kazuuji, under Hideyoshi, moved into the site. It is believed that Hideyoshi ordered Kazuuji to have the castle keep built and decorated as he liked.

After the death of Hideyoshi in 1598 and the Battle of Sekigahara in 1600, Ieyasu unified Japan and founded the Tokugawa Shogunate in Edo in 1603.

According to history books, after Ieyasu retired as Shogun in 1605, he returned to Sunpu Castle and started renovations from 1607.

The upper part of the stone foundation showed signs of deliberate deconstruction and was buried under the newer foundations. The gilt tiles were found in the older moat that had been filled up, indicating some measure of disrespect.

The gilt roof tiles were a "symbol to show (Hideyoshi's) majesty to Ieyasu," said Hitoshi Nakai, a professor of archeology at the University of Shiga Prefecture.

"It can be understood that Ieyasu covered over the keep foundations built by Kazuuji and built a new one at the time of extensive renovations to demonstrate his clan's power after the change in administration."

The public is invited to view the remnants of the older stone foundation on Oct. 20 and 21. The site will be formally open to the public along with the gold-gilt roof tiles from Nov. 22.

(This article was written by Etsuko Akuzawa and Takafumi Yabuki.)