CastleHilltop castle (hirayamajiro)Next 100 Fine Castles No. 148
What makes this castle distinctive
The castle where Hojo Soun launched his rise went on to change hands among more than 16 lords and commanders in 120 years on a contested border.
Why?
Kokokuji Castle is said to be the first castle held by Ise Sozui, better known as Hojo Soun, founder of the Hojo clan that later ruled the Kanto region. It stood on the border of Suruga and Izu beside the Negata road, so after Soun left it was fought over by the Imagawa, Hojo, Takeda, Tokugawa and Toyotomi sides. Excavated finds date from the late 15th to the early 17th century, matching the records of its long use.[1][2][3]
North of the main enclosure, directly behind the reputed keep base.
What to look at
The width and depth of the dry moat, more than 20 m across.
Why it's interesting
Numazu City names this great moat and the massive earthen banks as the castle's main sights. Excavations show the moat was dug in a major rebuilding after the late 16th century, along with the keep base and the turret platforms on either side.[1][2]
The raised ground north of the main enclosure, behind Homi Shrine.
What to look at
The stone wall facing the raised platform; some split stones show chisel marks.
Why it's interesting
Excavations showed the wall is about 20 m wide and 5 m high. It is thought to date from after Toyotomi Hideyoshi unified Japan, when only especially important castles in today's Shizuoka had stone walls. Two foundation-stone buildings were found on top, but not one roof tile, so it was probably not a tiled keep.[1][2][3]
Can you see it?
Visible from outsideVisible from outside; ongoing excavations can change what you see.
The massive earthen banks around the main enclosure
Where
Around the main enclosure (honmaru).
What to look at
The high earthen walls that ring the honmaru, and the view down into the castle from their tops.
Why it's interesting
Edo-period maps show the main enclosures ringed by earthen banks (dorui), and most of them survive. From the west turret platform you can see the town of Hara and Suruga Bay.[1][2]
Can you see it?
Visible from outsideIn places you can walk along the top of the banks.
At a glance for visitors
Nearest station
30 min walk from JR Hara Station
Climb
Some climbing
Time neededEditors' estimate
About 45 minutes to an hour to walk around the site.
Admission
Free
Hours
9:00–21:00 (until 17:00 on Mondays and the day after a national holiday)
Access
Open to visitors
The site is open to explore. The Next 100 Castles stamp is outdoors beside the information board in the grounds of Homi Shrine in the main enclosure (available all day) and at the Ukishima Community Center. The area is residential, so be considerate early and late.
The castle sits at the tip of a ridge running south from Mount Ashitaka. The Negata road passing to the south was a main route linking toward Hakone and Ashigara. The land south and on both sides was marsh where water rises if you dig even a meter, and it seems to have served as a natural moat.[2][3]
02
Tradition
Where Hojo Soun began
Ise Sozui was an official of the Muromachi shogunate whose sister had married into the Imagawa family. For helping his nephew Imagawa Ujichika win a succession dispute, he is said to have received twelve villages in Fuji district and Kokokuji Castle around 1487. In 1493 he attacked Ashikaga Chachamaru, the shogunal deputy based at Horigoe in Izu, from here, and later moved his base to Nirayama Castle. This attack is often called the start of the Warring States period in eastern Japan.[1][2][4]
03
Historical record
A castle that grew with every war
In 1549 Imagawa Yoshimoto moved the temple of Kokokuji that stood on the site and properly fortified the castle. The Hojo and Takeda then fought over it, and in the late 16th century a maru-umadashi, a crescent-shaped moat and bank guarding the gate typical of Takeda castles, was built while the moats were more than doubled in width. After the Takeda fell, the castle passed to the Tokugawa.[2][4]
04
Historical record
The last lord walks away
When the Hojo fell in 1590, Kawake Shigetsugu, a retainer of the Toyotomi general Nakamura Kazuuji, became lord, and after the Battle of Sekigahara Tokugawa Ieyasu's retainer Amano Yasukage took over in 1601 with a domain worth 10,000 koku. Under Kawake and Amano the castle was rebuilt toward an early modern form with stone walls, a keep base and the great moat. But in 1607, after his retainers killed or wounded farmers from shogunate land, Yasukage abandoned the castle and fled, and Kokokuji Castle was shut down.[1][2][3]
05
Historical record
Revealed little by little through excavation
Since a survey of the keep base in 1982, more than 20 excavations covering over 20,000 square meters have been carried out across the site. It became a National Historic Site in 1995, covering about 110,000 square meters, among the largest in the prefecture. It was chosen for the Next 100 Fine Castles of Japan in 2017, and Numazu City continues excavating as it plans a historic park. Some parts have changed over time; for example, today's prefectural road (the Negata road) now runs straight through the third enclosure.[1][2][4]
The raised platform traditionally called the keep base held two foundation-stone buildings but yielded no roof tiles, so it probably did not carry a tiled keep; hence it is called the reputed keep base.
The site today
At the end of a ridge below Mount Ashitaka, the level enclosures, earthen banks and dry moats of the main, second and third enclosures survive. There are no buildings; Homi Shrine stands in the main enclosure. Part of the north enclosure was destroyed by the Shinkansen line, and a prefectural road crosses the third enclosure.
Main buildings
Site only
Foundation-stone buildings on the reputed keep base
Excavations found a large gate on foundation stones and a stone-lined drain.[2]
Key facts
Type
Castle
Setting
Hilltop castle (hirayamajiro)built on a low hill rising from the plainEditorial article
Period
Medieval (c.1185–1570s), Early modern (1570s–1871)Editorial article
Keep (tenshu)
Not yet confirmedwhether a keep existed is still being checkedEditorial article
Main lords
Tokugawa clan, Matsudaira clan, Ise clan, Takeda clan, Hōjō clan, Imagawa clanJapan Castle Foundation
Abandoned
1607Wikipedia (ja)
Remains to see
Stone walls, Earthen ramparts, Moats, Baileys / enclosures (kuruwa), Keep base (tenshudai), Fortified gateways (koguchi)Editorial article
Designation
National Historic Site (Kokokuji Castle ruins) (1995)Editorial article
Selection
Next 100 Fine Castles No. 148Japan Castle Foundation
Visiting
Access
Open to visitors
The site is open to explore. The Next 100 Castles stamp is outdoors beside the information board in the grounds of Homi Shrine in the main enclosure (available all day) and at the Ukishima Community Center. The area is residential, so be considerate early and late.
From Surugawan-Numazu Smart IC (westbound) via Prefectural Road 22, or from Ashitaka Smart IC (eastbound). Parking availability not confirmed.[1]
Checked: 2026-10-03
Grounds opening hours
Open at all times (please be considerate of neighbors)[1]Checked: 2026-10-03
Time neededEditors' estimate
About 45 minutes to an hour to walk around the site.
Steps, slopes and footing
A ridge-end castle; reaching the main enclosure and keep base involves slopes and climbing over earthen banks.[2]
Wheelchairs and strollers
Not confirmedChecked: 2026-10-03
Toilets and rest
Not confirmed
English signs / audio guide
No official English guide was found.
Seasons
On clear days the west turret platform and keep base look out over the town of Hara and Suruga Bay.[1][2]
Photography
Not confirmed
Works, closures and restrictions
Excavations for site improvements are ongoing, so access and what you can see may vary.[1][3]Checked: 2026-10-03
Editors' guide
An editorial guide based on sources and confirmed information — not a first-hand visit report.
Who will enjoy it
Good for anyone interested in Hojo Soun and the beginning of the Warring States period, and for fans of earthen castles with big banks and moats.
What makes it interesting
Stand on the great banks around the main enclosure, then compare the stone wall of the keep base with the 20-plus-meter moat behind it. You can see how Toyotomi-era stonework was added to an earthen castle.
Before you go
There are almost no buildings or visitor facilities. Reading Numazu City's guidebook (PDF, Japanese) beforehand makes the remains much easier to understand.
Ways to enjoy it
Climb from behind Homi Shrine to the keep base and look toward Suruga Bay to imagine how the castle watched both the Negata road and the coastal Tokaido.
Photos
Visitor reviews
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Open questions
The oldest sources saying Soun held Kokokuji are Edo-period war tales and family histories, and Numazu City notes they must be read with care. The date is given as both 1487 and 1488.
Soun never called himself Hojo Soun; he used the names Ise Shinkuro Moritoki and later Ise Sozui.
Excavated finds cannot tell whether the final rebuilding was done by Kawake Shigetsugu or Amano Yasukage.
Parking, toilets and accessibility information could not be confirmed.
YaritsusozaiCC BY-SA 4.0Wikimedia Commons
