Kuroi Castle Ruins: A Sengoku Fortress on Mount Inokuchi
The summit of Mount Inokuchi rises 356 meters above the town of Kasuga in Tamba, and the bare stone walls scattered across its crown are nearly all that survives of one of the most stubbornly held mountain castles of Japan's warring states era. Kuroi Castle, also recorded under the older name Hozuki-jo, once spread across the whole mountain. Its lord, Akai Naomasa, held off the famous general Akechi Mitsuhide here long enough to be remembered as the Red Ogre of Tamba.
Today the mountain belongs to hikers and history travelers. The climb from the foot of the hill to the main bailey takes well under an hour, and the view from the top reaches across the Tanba basin, the same ground the defenders once watched for approaching armies.
The site became a National Historic Site on August 11, 1989. In 2017 it was also chosen as number 163 on the Continued Top 100 Castles of Japan, the sequel list to the country's better-known hundred.
From the Akamatsu to the Red Ogre of Tamba
The castle's story reaches back to the fourteenth century. Local tradition credits Akamatsu Sadanori, second son of Akamatsu Norimura, with first fortifying the summit after he received the Kasukabe estate in Hikami District. The Akamatsu held the heights for roughly two hundred years before the Ogino family took their place as castellans.
The man who shaped the castle into the form visible today arrived in 1554. In that year Akai Naomasa, himself born of the Ogino line, defeated Ogino Akikiyo, seized Kuroi, and adopted the name Akuemon. He went on to command the combined Akai and Ogino forces, and in 1565 he killed Naito Sosho, the powerful deputy military governor of Tanba. Holding Hikami along with the neighboring Amata and Ikaruga districts and part of Funai District, Naomasa pressed his influence into the provinces of Tango and Tajima. The fortifications now traced in stone across the mountain were largely finished during these years.
His standing reached the imperial capital. Around 1568 the former regent Konoe Sakihisa is said to have stayed at the castle, and the Akai family genealogy records that one of Sakihisa's daughters married Naomasa.
Two Sieges and the Fall of the Castle
In 1570 Naomasa accepted Oda Nobunaga's confirmation of his grip on the three inner districts of Tanba. The understanding did not hold. From the early 1570s he turned against Nobunaga, exchanging messages with Takeda Katsuyori, the warrior monks of Ishiyama Hongan-ji, and the Mori clan through Kikkawa Motoharu.
Nobunaga ordered Akechi Mitsuhide to subdue Tanba in 1575. That October, Naomasa abandoned Takeda Castle in Tajima, fell back to Kuroi, and let Mitsuhide lay siege. The defenders held for three months. Then, in the middle of the first month of 1576, Hatano Hideharu, who until then had been fighting on Mitsuhide's side, suddenly struck his headquarters. Mitsuhide's army collapsed and fled. This reversal is one reason the castle is still talked about.
Naomasa died of illness in 1578. His younger brother Akai Yukiie took command as guardian of the young heir, but the Akai cause was weakening. Mitsuhide came back in 1579, this time reinforced by Hashiba Hidenaga. The castles of Hikami fell one after another, Kuroi was cut off, and in the eighth month the fortress surrendered. The campaign that ended here is described in detail in the Shincho-koki, the chronicle of Nobunaga's career.
Because the stone ramparts and earthworks of the 1560s and 1570s were never rebuilt in a later style, the ruins keep a clear record of a Sengoku mountain castle frozen at the point when the country was being unified. That undisturbed quality is the main reason for the national designation.
What to Look For on the Mountain
The core of the castle runs about 150 meters along the ridge, divided from north to south into the main bailey (honmaru), the second bailey (ni-no-maru), and the third bailey (san-no-maru). A step below them lie flatter terraces called the east, west, and belt baileys.
The stonework is what most people climb to see. The walls were built by the nozura-zumi method, rough natural stones piled up without dressing, typical of the mid-sixteenth century. Between the main and second baileys stands a wall roughly 30 meters long and 5 meters high. Study its corners and you can pick out sangi-zumi, the technique of stacking long and short stones in alternation to brace an angle. One detail worth knowing: the heaviest masonry faces the town side rather than the rear, which has led historians to suspect the walls were meant to impress the valley below as much as to hold off an attack.
The defenses do not stop at the summit. Smaller baileys spill down the slopes with names such as the drum terrace (taiko-no-dan) and the stepping-stone terrace (ishifumi-no-dan), and the ridges radiating from the peak end in outlying forts: Senjoji to the north, Ryugahana and the Hyakken-baba parade ground to the east, and Matoba to the south. Walking even part of this network makes the scale of the fortress plain.
From the top the basin opens in every direction. On cold, still mornings in autumn and winter a sea of clouds sometimes fills the valley, which has won Kuroi a place among the region's so-called castles in the sky.
The Town Below and How to Reach the Castle
At the foot of the mountain sits Kozen-ji, a temple built on the site of the castle's lower residence. After Kuroi fell, Mitsuhide's senior retainer Saito Toshimitsu moved into this compound. His daughter, born here in 1579, grew up to become Kasuga no Tsubone, the formidable wet nurse and chief lady-in-waiting to the third Tokugawa shogun. She is said to have spent her earliest years in Kasuga, and the temple grounds, themselves a National Historic Site, keep her story alive. A stone she is said to have sat on still stands in the precinct.
Reaching the castle is easy by the standards of mountain sites. Trains on the JR Fukuchiyama Line stop at Kuroi Station, and the trailhead behind Kuroi Elementary School is about a ten-minute walk away. Two paths climb the hill, one gentle and one steep, and they meet partway up before reaching the main bailey. Sturdy shoes make sense, and walkers should know that bears are occasionally reported on the slopes in autumn.
Every November the town holds the Kuroi Castle Festival, when local people parade in handmade armor. Stamps and goshuin seals for castle collectors are issued not on the mountain but at the Kasuga Resident Center and other public facilities down in town.
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Q&A
- How long does the climb take?
- From the trailhead near Kuroi Elementary School, the main bailey is roughly 40 minutes to an hour away, depending on the route. The steep path is shorter but demanding; the gentler path is kinder underfoot. Many visitors go up one way and come down the other.
- Why was Akai Naomasa called the Red Ogre of Tamba?
- The nickname reflects his reputation as a fierce and feared commander in western Tanba. He defeated rival warlords, expanded into neighboring provinces, and famously withstood Akechi Mitsuhide's first siege of Kuroi, all of which gave the name its weight.
- What is the connection to Kasuga no Tsubone?
- After the castle fell, Saito Toshimitsu occupied the lower residence at the foot of the hill, now Kozen-ji temple. His daughter was born there in 1579 and later became Kasuga no Tsubone, the influential wet nurse of the third Tokugawa shogun. The temple is treated as part of the historic site.
- Is there anything to see at the top besides the view?
- Yes. The summit keeps long stretches of uncoursed stone wall, including a section about 30 meters long with reinforced corners, along with the clearly marked baileys of the main castle. The smaller terraces and outlying forts on the surrounding ridges reward anyone willing to explore further.
- When is the best time to visit?
- Autumn offers comfortable hiking and the chance of a sea of clouds on cold mornings, and November brings the castle festival to the town below. Spring is pleasant as well. Summer climbs are best done early in the day, and caution about bears is advised in the autumn months.
Basic Information
| Name | Kuroi Castle Ruins (Kuroi-jo ato), also known as Hozuki-jo |
|---|---|
| Location | Kasuga-cho, Tamba City, Hyogo Prefecture |
| Designation | National Historic Site |
| Designation Date | August 11, 1989 |
| Setting | Summit of Mount Inokuchi, elevation 356 meters |
| Period | Sengoku period; principal stonework completed in the 1560s to 1570s |
| Other Selection | Continued Top 100 Castles of Japan, No. 163 (selected 2017) |
| Access | About a 10-minute walk from JR Kuroi Station (Fukuchiyama Line) to the trailhead, then 40 to 60 minutes on foot to the main bailey |
| Related Site | Kozen-ji temple at the foot of the mountain, on the lower residence site (also a National Historic Site) |
| Admission | Open mountain site; no admission fee. Stamps available at the Kasuga Resident Center. |
References
- Database of National Cultural Properties (Agency for Cultural Affairs): Kuroi Castle Ruins
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/1900
- Tamba City Tourism Association: Kuroi Castle Ruins
- https://www.tambacity-kankou.jp/spot/spot-1530/
- Tamba City: Continued Top 100 Castles Stamp Location for Kuroi Castle
- https://www.city.tamba.lg.jp/soshiki/shakaikyoikubunkazaika/gyomuannai/7/2747.html
Last verified: 2026.05.28