Between the late Heian Age (794 - 1185) and the Kamakura Age (1185 - 1333) . Nirayama in Shizuoka Prefecture was the base of the HOJYO Clan, who were in the position of the regency to support, After the third "Shogun", MINAMOTO -NO Sanetomo (1192 - 1219) was assassinated in 1219, the HOJYO Clan took the helm of Kamakura Bakufu.

There are a couple of historical sites related the HOJYO Clan in Nirayama:
http://handejapan19.html.xdomain.jp/TravelDestinations/Chubu/HojyoClan_E.html

There are also historical sites in the Muromachi Age (1336 - 1573) in Nirayama. Nirayama Castle was one of them.

The ruins of Nirayama Castle are located very close to Hiruga-Kojima. You will see the hill where the ruins of Nirayama Castle are located from Hiruga-Kojima.

It is considered that Nirayama Castle was built between 1469 and 1486. In 1493, HOJYO Soun (1456? - 1519) attached Horikoshi-Gosho, which was the government office of the Muromachi Bakufu, located in Nirayama, and killed ASHIKAGA Chachamaru (1469 - 1498) , who was a brother of ASHIKAGA Yoshizumi (1481 - 1511) , the eleventh Shogun of the Muromachi Bakufu. HOJYO Soun expand his territory to Izu Peninsula and moved to Nirayama Castle.

HOJYO Soun originally named ISE Moritoki, and he was nothing to do with the HOJYO Clan, who governed the area of Nirayama in the late Heian Age (794 - 1185) and the Kamakura Age. The descendants of HOJYO Soun were named the "GO-HOJYO" Clan to distinguish from the original HOJYO Clan.

If you walk into the ruins of Nirayama Castle, you will see the narrow slop which is cut through the hill. The wall of the slop is very sharp. This is the artificial excavation to gather the enemies in to the excavation. The solders in the castle could easily attach enemies gathered in an artificial excavation.

When passing through the artificial excavation, Japanese ascot flowers broomed along the pond in the east side of the castle. The pond behind the castle worked as a moat to prevent enemies to approach to the castle.

You will see tall earthen walls in the third bailey.

Behind the earthen walls, you will see Nirayama High School. The schoolyard is located at the site of the palace building of Nirayama Castle.

To the south, Kumano Shrine is located. The shrine was built by HOJYO Soun in 1500.

Finally, you will arrive at the main bailey at the top of the hill. The altitude of the main bailey is forty-nine meters.

You will see Mt. Fuji from the main bailey.

HOJYO Soun expand his territory to the east. After HOJYO Ujituna (1487 - 1541) , who was the son of HOJYO Soun, moved the base from Nirayama Castle to Odawara Castle in 1518, Nirayama castle became the important base to protect the west of GO-HOJYO's teritory against the IMAGAWA and the TAKEDA Clans.

In 1590, TOYOTOMI Hideyoshi (1537 - 1598) , who governed almost all areas of Japan in the late sixteen century, attacked the GO-HOJYO Clan. More than fifty thousand soldiers of Hideyoshi's troops attached Nirayama Castle. The GO-HOJYO Clan became extinct by Hideyoshi's expedition. Nirayama Castle became abandoned in 1601.

Please refer the page of "Ruins of HOJYO Clan in Nirayama":
http://handejapan19.html.xdomain.jp/TravelDestinations/Chubu/HojyoClan_E.html

The ruins of Horikoshi-Gosho are located at the foot of Mt.Moriyama in Nirayama. In 1458, ASHIKAGA Yoshimasa (1436 - 1490) and the (1435 - 1491) as the "Kamakura Kubo", the government director of the Muromachi Bakufu. As the power of Muromachi Bakufu was very weak, ASHIKAGA Masatomo could not go to Kamakura and built a government office in Nirayama. This was Horikoshi Gosho.