Kōkokuji Castle: A Sengoku Frontier Fortress in Japan
Site at a Glance
- Rating
- 3.9
- Popularity
- Low
- Country
- Japan
- Primary era
- Early Modern
- External website
- Open
- Eras represented
- Early Modern
- Civilizations
- Later Hōjō, Takeda, Tokugawa
- Site type
- Military
- Remains
- Castle
On this page15 sections
History
Kōkokuji Castle was a Japanese Sengoku-period fortress in Japan, at Negoya in Numazu, Shizuoka, built and repeatedly reshaped during the era of intense competition among regional warlords in the fifteenth and sixteenth centuries. It occupied the eastern frontier of Suruga Province and took its name from the Buddhist temple Kōkokuji, which had previously stood on the site.
Origins and the Imagawa frontier
The castle’s foundation date remains uncertain, although it is generally placed in the late fifteenth century. Later tradition connects the site with Ise Moritoki, better known as Hōjō Sōun, who is said to have supported Imagawa Ujichika in a succession dispute in 1487. In return, he supposedly received territory and made Kōkokuji Castle his base. This association is not confirmed by contemporary records, and the territory attributed to him is also uncertain. Some interpretations instead connect Moritoki with a separate enclosure west of the castle or with another part of the present complex.
When Moritoki later moved to Niirayama Castle after taking control of Izu Province, his senior retainer Tominaga Masanao was traditionally appointed castellan of Kōkokuji. The earliest contemporary documentary evidence for the castle dates to 1549. By then, the Suruga region was contested by the Imagawa, Takeda, and Hōjō clans, and the fortress had become part of a changing network of frontier defenses.
Conflict and Imagawa reorganization
A later tradition states that in 1537 the Hōjō officer Aochi Hida defected to Takeda Nobutora and that Kōkokuji was then transferred to the Imagawa as part of a marriage settlement. Because the castle’s early construction history is uncertain, this episode cannot be securely established. The wider region was certainly affected by warfare. In 1545, Imagawa Yoshimoto, allied with Takeda Shingen and Uesugi Norimasa, attacked Hōjō positions in Suruga and Musashi and recovered Sunto District through a negotiated settlement. A record from 1558 states that Osenji Temple, about 1.4 kilometers west of the castle, had repeatedly burned and suffered severe damage during the conflict.
In 1549, Imagawa Yoshimoto ordered Kōkokuji Temple to be relocated and designated the temple and its surrounding fields as castle grounds. A substantial fortress was probably established or reorganized at this time. The three-clan alliance formed in 1554 between the Takeda, Hōjō, and Imagawa temporarily eased regional tensions. Its negotiations may have been connected with rebuilding at Kōkokuji, and one interpretation places a meeting traditionally associated with Zentokuji Temple at the castle instead.
The earliest identifiable castle phase centered on the southern Third Enclosure, beside the Negata Road, and extended north through the Second Enclosure toward the southern entrance of the Main Enclosure. This arrangement probably existed by the middle of the sixteenth century, when the castle projected into marshy ground.
Hōjō and Takeda control
In December 1568, Takeda Shingen broke the three-clan alliance and invaded Suruga. Hōjō Ujiyasu sent troops west to support the Imagawa, took Kōkokuji Castle into Hōjō territory, and appointed Hawa Ujitsugu as castellan and later lord. Ujitsugu remodeled the fortress. A letter issued by Hōjō Ujimasa in January 1570 confirms that he had successfully defended it against a Takeda attack.
The Takeda and Hōjō alliance was renewed in 1571, and Kōkokuji Castle was transferred to the Takeda. During renewed fighting in 1579, Takeda Katsuyori built Sanmaibashi Castle at Numazu Port near the Hōjō frontier and stationed the senior retainer Kasuga there. Kōkokuji then served as a rear base, supporting the Takeda position farther from the immediate line of conflict.
Tokugawa and Toyotomi phases
After the fall of the Takeda in March 1582, Kōkokuji became Tokugawa territory. Tokugawa Ieyasu first assigned Makino Yasunari to the castle and later placed Matsudaira Kiyomune of the Takeya-Matsudaira family there with an income of 2,000 kan, a historical unit used in assessing revenue.
When Ieyasu was transferred to the Kantō region in 1590, Kawake Shigetsugu, a retainer of Nakamura Kazuuji, served at Kōkokuji under Toyotomi rule in Suruga. Surviving documents record Shigetsugu’s confirmation of temple lands belonging to Osenji and Ashitaka Myōjin. During this period the castle was expanded and remodeled to accommodate substantial forces. Its strategic purpose included checking Ieyasu after his transfer to the Kantō, although the Battle of Sekigahara later reduced its military importance.
In 1601, Amano Yasukage, a Tokugawa founding retainer, became lord of Kōkokuji Castle with an income of 10,000 koku, a rice-based measure of domain revenue. Kōkokuji Domain was established under his administration. After taking responsibility for a problem in his territory and becoming dissatisfied with the resulting judgment, Amano left the domain. The domain was confiscated, and the castle was abandoned in March 1607.
The ruins were designated a National Historic Site on March 17, 1995. In 2017, Kōkokuji Castle was selected as site number 145 in the Continued Top 100 Japanese Castles. Restoration and reconstruction work is currently being undertaken at the site.
Remains
Kōkokuji is a hirayama castle, a fortification built on a hill or low mountain beside flatter ground, with linked fortified enclosures arranged along a north-south line. From north to south, the principal areas were the North Enclosure, the enclosure traditionally called the Tenshu Platform, the Main Enclosure, the Second Enclosure, and the Third Enclosure. The Shimizu Enclosure lay to the east. The complex covered roughly 60 meters from east to west and 50 meters from north to south, at an elevation of about 36 meters.
Setting and enclosure layout
The castle occupies the southern foothills of the Ashitaka Mountains. Deep valleys and steep valley walls protected its eastern and western sides, while the former Ukishimagahara wetlands guarded the south. A small alluvial fan connected the foothills with the wetlands and provided the terrain on which the fortress was built. The east-west Negata Road followed the foothills, while another road ran south from below the castle across Ukishimagahara toward Senbon Beach. Their intersection made the site an important transport junction.
A thick loam layer covers the foothills. The enclosure surfaces generally use the upper Chubu Loam, a black band, or a scoria layer. These hard strata reduced the need to strengthen the ground and were incorporated into the castle’s construction. The Main Enclosure occupied the highest ground and may have held a tenshu, the principal tower of a Japanese castle. No surviving tower has been confirmed. A stone platform east of the Main Enclosure is associated with a cannon.
An early Edo-period map appears to represent the castle’s final phase and broadly matches the surviving remains. It does not include the North or Shimizu enclosures, indicating that these areas had ceased to be used by the beginning of the Edo period. Both were probably added during the second half of the sixteenth century. A round earthwork entrance and a crescent-shaped moat suggest that this phase was associated with Takeda construction and shifted the defensive center toward the mountains as conflict with the Hōjō intensified.
During the Tokugawa phase, the castle reached its greatest extent, running from the Third Enclosure to the North and Shimizu enclosures. Under Toyotomi rule, the Tenshu Platform formed the northern limit and the Third Enclosure the southern limit, while the North and Shimizu enclosures lay outside the castle. Stone walls and a tower were positioned where they could be seen from the Tokaido and Negata Road, giving the later fortress a more conspicuous representative character.
Main and Second Enclosures
Stone buildings and wall
Two foundations of stone-built structures have been identified. The western building had two parallel rows of stones. The eastern building had an L-shaped outer arrangement along its southern and western sides, with additional stones inside. No roof tiles were recovered from either foundation. A wall made from naturally shaped, uncut stones measures about 24 meters along its top, 13 meters at its base, and is estimated to have stood 4 meters high. It survives above ground on the eastern part of the southern face, while stones were removed from the western section.
Gate, drainage, and bridge
A gate site measures approximately 5.4 meters from east to west and 3.6 meters from north to south. The base of an earthen rampart about 20 meters wide runs east-west. A stone-lined drainage channel extends for about 60 meters, incorporating stone reused from a Buddhist commemorative pagoda. Another drainage ditch, about 4 meters long, lay outside the northern line of the stone foundations.
One dry moat is about 13 meters wide and reaches 7 meters in depth beside the Main Enclosure and 3 meters beside the Second Enclosure. Its lower section is V-shaped and becomes box-shaped at an intermediate level. Irregularities on the moat floor probably reflect later remodeling. An earthen bridge survives where the middle loam layer was left in place during excavation. It is about 7 meters wide on the Second Enclosure side, 5 meters wide on the Main Enclosure side, and 10 meters long.
Moats and northern defenses
Crescent-shaped moat
The crescent-shaped moat measures about 37.8 meters in length, reaches 4.3 meters in width at its widest point, narrows to 0.8 meters at the bottom, and is 3.8 meters deep. Its profile is V-shaped. Pottery from the moat includes a grinding bowl made during the third stage of the Ōgama sequence, an archaeological classification of pottery-production stages, dated to the 1570s through the 1590s. Other pieces belong to the first and second stages, with one contemporary with the fourth stage. Much of another crescent-shaped moat was destroyed during construction of the Shinkansen railway. Its date remains unknown because no artifacts were recovered from the surviving section.
Dry Moats 1 and 2
Dry Moat 1 bends around an earthen bridge near the point thought to have been the center of the crescent-shaped moat. West of the bridge, it is V-shaped, about 13 meters wide at the top, 1 meter wide at the bottom, and 7 meters deep, with a step at roughly 2 meters. East of the bridge, it is box-shaped, about 12 meters wide at the top, 1.3 meters wide at the bottom, and 5.4 meters deep, also with a step at about 2 meters. The bridge and moat resemble another excavated dry moat in their shape and sedimentation.
Dry Moat 2 runs almost parallel to Dry Moat 1 and is approximately 10 to 13 meters wide at the top. Its bottom has not been excavated. Fill deposited from the south contains fragments of bedrock from the lower loam layer. Another moat bends at three points and represents a double moat formed by re-excavation. A round dish recovered from it belongs to the second stage of the Ōgama sequence.
Large and cut moats
A large moat ranges from about 22 to 30 meters in width and from 15 to 20 meters in depth. It has two levels, a V-shaped bottom, and a box-shaped section on the north. Cut into the lower loam, it overlies an older moat, indicating that the surviving feature was re-excavated. A separate cut moat is about 13 meters wide and survives to a depth of 4.5 meters in a V-shaped form. It was later reshaped into a box-shaped moat 2.8 meters deep, bends twice, and follows almost the same line as the earlier large dry moat. A group of pits was also identified nearby.
Ramparts and earlier occupation
A pair of parallel earthen ramparts contained a Shitoro grinding bowl, from a regional ceramic tradition, dating to around the end of the sixteenth century. They also held grinding bowls and unglazed drinking vessels from the final quarter of that century. Beneath the ramparts were pits containing fragments of round dishes from earlier Ōgama stages, a rammed-earth feature with ash-glazed pottery and oil-lamp dishes, and a ditch-like feature.
Mixed pottery from the area traditionally identified as the Eastern Boat Landing reflects activity over a long period. The finds include Jomon pottery; Middle Yayoi jars and bowls; Late Yayoi jars, cooking vessels, and Haji ware; Early and Late Kofun vessels; and cups, cooking vessels, and Sue ware from the Ritsuryō period, Japan’s ancient centralized administrative system based on legal codes. Other finds include ceramics, porcelain, earthenware such as tea bowls, jars, and grinding bowls, and stone tools of uncertain date.
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