CastleMountain castle (yamajiro)Japan's 100 Fine Castles No. 72
What makes this castle distinctive
Mori Motonari turned an entire mountain into a castle, and ruled from its summit until the day he died.
Why?
Koriyama Castle began as a small fort on a ridge near the southeast foot of the mountain. Under Mori Motonari it spread over the whole of Mount Koriyama, about 400 m high, with more than 300 terraced enclosures (kuruwa) cut along 12 ridges and the valleys between them, radiating out from the summit. After handing the family leadership to his son, Motonari moved up to the summit and lived and governed there until his death.[1][2]
The top of Mount Koriyama (about 390 m), where the main, second and third enclosures run together.
What to look at
The roughly 35 m square main enclosure (honmaru) and the raised turret platform (23 m by 10 m) at its north end; the low stone walls of the second enclosure and the stepped levels of the third, the largest enclosure in the castle.
Why it's interesting
No buildings remain, but the leveled terraces, earthen banks and traces of stone walls are clear, showing how a warring-states mountain castle turned a whole mountain into a fortress. The summit stands about 190 m above the foot.[2]
Can you see it?
Visible from outsideReached on foot by mountain trail (free). Watch your step.
Mori Motonari's grave and the Hyakuman Isshin monument
Where
On the southwest slope of the castle, at the site of Toshun-ji temple.
What to look at
Motonari's grave, the Mori family graves on the level below, and the nearby Hyakuman Isshin monument.
Why it's interesting
Motonari died in 1571 at the age of 75 and was buried here. Some of the stone lanterns before the grave were donated by later figures such as Asano Yoshinaga, lord of Hiroshima. The nearby monument recalls a legend that, when expanding the castle, Motonari had a stone carved with "Hyakuman Isshin" ("a million people, one heart") buried instead of a human sacrifice.[3]
Can you see it?
Visible from outsideOpen to visit. A memorial rite is held every July 16.
03
Honjo, the original castle Motonari first entered
Where
The southeast foot of Mount Koriyama (293 m above sea level, about 90 m above the plain).
What to look at
The turret platform at its western end and the trench (horikiri) cut through the valley behind it.
Why it's interesting
When Motonari became head of the Mori family in 1523, this is the castle he moved into, and it stayed the center of Koriyama Castle until he expanded it over the whole mountain. It preserves the form of an early warring-states mountain fort well; compare it with the summit to see how much the castle grew.[2]
Can you see it?
Visible from outsideOpen to visit.
At a glance for visitors
Nearest station
5 min walk from Akitakata City Hall bus stop
Climb
Steep climb
Time neededEditors' estimate
Around 2 hours to climb to the summit and back; half a day if you also visit the museum.
Admission
Adults (15 and over) 500 yen; free for junior high students and younger (cash only; includes special exhibitions)
Hours
9:00–17:00
Access
Open to visitors
The castle site is free to explore on mountain trails. The Koriyama Castle Historic Site Guide Association offers guided tours (application required). The Japan 100 Castles stamp is at the reception of the Akitakata City Museum of History and Folklore during opening hours; on museum closing days it is at the city Board of Education's Lifelong Learning Division, 9:00–17:00, except December 29 – January 3.
After Mori Tokichika came to Yoshida in Aki Province in 1336, during the Northern and Southern Courts period, the Mori built a castle (Honjo) at the southeast foot of Mount Koriyama, though exactly when is unknown. From then until they moved to Hiroshima Castle in 1591, Koriyama remained the Mori family's home base.[1][3]
02
Historical record
Holding off the Amago army
From 1540 into the New Year of 1541, the Amago clan of Izumo attacked Koriyama Castle with a large army. Motonari is said to have held out with some 8,000 people, farmers included, and driven the Amago away. At that time the castle had not yet spread over the whole mountain.[6]
03
Historical record
Motonari expands the castle over the mountain
Motonari, who became head of the Mori in 1523, expanded the castle over all of Mount Koriyama in the mid-16th century. It stretched about 1.1 km east to west and 0.9 km north to south, with an inner moat around the southern foot and more than 270 leveled terraces, plus temples, inside. Roads and markets were laid out below, forming a castle town.[1][3]
04
Historical record
The move to Hiroshima
Motonari's grandson, Mori Terumoto, built a new castle at Hiroshima near the sea and moved there in 1591, ending Koriyama's role as the family seat. In the Edo period the castle was demolished, and its stone walls are said to have been pulled down too. No buildings survive, but the terraces, earthworks, traces of stone walls and the graves of Motonari and the Mori family remain.[3][6]
05
Historical record
A National Historic Site with a museum below
The castle site became a National Historic Site in 1940 and is now designated together with Tajihi-Sarukake Castle as the "Mori Clan Castle Sites." At the foot of the mountain, the Akitakata City Museum of History and Folklore introduces the Mori family and the castle. A section of stone wall at Toridani, uncovered during excavations after heavy rain caused a collapse, has been preserved and can be viewed as found.[3][4][6]
The Japanese Castle Association lists no keep. Some say Terumoto built a three-story keep, but nothing certain is known.
The site today
The whole of Mount Koriyama is the castle site. No buildings remain, but terraces, earthworks, trenches, traces of stone walls and the graves of Motonari and the Mori family survive along mountain trails. The town of Yoshida and the city history museum lie at the southern foot.
Main buildings
Site only
Main enclosure (honmaru)
At the summit, about 35 m square, with a turret platform at the north end.[2]
Site only
Third enclosure
The largest enclosure (about 1,400 m²), with remains of stone walls.[2]
Site only
Honjo (original castle)
At the southeast foot; preserves the form of an early warring-states fort.[2]
Site only
Toridani stone wall
Excavated stone wall, preserved and open to view.[3]
Key facts
Type
Castle
Setting
Mountain castle (yamajiro)built on a mountain; expect a climbEditorial article
Period
Medieval (c.1185–1570s)Editorial article
Keep (tenshu)
Keep lostthe castle had a keep, but it no longer stands (its stone base may remain)Editorial article
National Historic Site (Mori Clan Castle Sites: Tajihi-Sarukake and Koriyama) (1940)Editorial article
Selection
Japan's 100 Fine Castles No. 72Japan Castle Foundation
Visiting
Access
Open to visitors
The castle site is free to explore on mountain trails. The Koriyama Castle Historic Site Guide Association offers guided tours (application required). The Japan 100 Castles stamp is at the reception of the Akitakata City Museum of History and Folklore during opening hours; on museum closing days it is at the city Board of Education's Lifelong Learning Division, 9:00–17:00, except December 29 – January 3.
Address
278-1 Yoshida, Yoshida-cho, Akitakata, Hiroshima 731-0501 (Akitakata City Museum of History and Folklore)[4]
Checked: 2026-10-03
Nearest stations and how to get there
Akitakata City Hall bus stopAbout 1 hour 25 minutes by bus from Hiroshima Bus Center (bound for Yoshida Shucchojo)
about 5 min walk · Steep climb
Five minutes on foot from the bus stop to the foot of the castle; from there, a mountain trail climbs to the summit.[1]
Checked: 2026-10-03
JR Mukaihara StationJR Geibi Line
Steep climb
About 20 minutes by taxi. Buses from Mukaihara to Yoshida do not run on Sundays and holidays and are infrequent on other days.[1]
Checked: 2026-10-03
Hours and admission
Akitakata City Museum of History and Folklore
Hours
9:00–17:00
Closed
Tuesdays (or the next day if Tuesday is a holiday), the day after national holidays, December 29 – January 3, and occasional closures
Admission
Adults (15 and over) 500 yen; free for junior high students and younger (cash only; includes special exhibitions)[4]
Checked: 2026-10-03
By car / parking
About 20 minutes from the Takata interchange on the Chugoku Expressway. Museum parking: 15 cars and 3 buses, free.[1][4]
Checked: 2026-10-03
Grounds opening hours
No set hours for the castle site were found.Checked: 2026-10-03
Time neededEditors' estimate
Around 2 hours to climb to the summit and back; half a day if you also visit the museum.
Steps, slopes and footing
The summit is about 190 m above the foot, reached by a mountain trail with rough sections.[2]
Wheelchairs and strollers
Not confirmedChecked: 2026-10-03
Toilets and rest
Not confirmed
English signs / audio guide
Not confirmed
Seasons
Koriyama Park (the former Kozen-ji site) at the foot is known for cherry blossoms. A memorial rite at Motonari's grave is held every July 16.[3]
Photography
Not confirmed
Works, closures and restrictions
As of the check date, no trail closures were announced. The museum is holding its 2026 autumn exhibition on the history of the Geibi Line in Akitakata.[7]Checked: 2026-10-03
Shrine at the foot of Mount Koriyama, the Mori family's place of prayer as the mountain's guardian in the warring states period. Its worship hall and main hall form a single building. The annual festival is on May 5.[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 fans of warring-states mountain castles, anyone tracing the life of Mori Motonari, and walkers who don't mind a climb.
What makes it interesting
Compare the stacked terraces running from the summit to the third enclosure with Honjo at the foot, and you see how a small fort grew into a mountain-wide castle. Also take in Motonari's grave, the Hyakuman Isshin monument, and the old well at Tsurii-no-dan west of the summit.
Before you go
This is a mountain castle site with no buildings, explored on foot along trails, so wear good shoes. The museum closes on Tuesdays; the 100 Castles stamp is available during its opening hours. Allow about an hour and a half by bus from central Hiroshima.
Ways to enjoy it
Visit the museum first to get the big picture of the Mori and the castle, then climb. For more depth, book a tour with the local historic site guides. Near the summit you can look down over the town of Yoshida.
Photos
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Open questions
The story of the buried Hyakuman Isshin stone is a legend, and the museum notes that the famous "three arrows" story is also of uncertain truth.
The 1540–41 siege, the Edo-period demolition and the 1940 designation year come from Wikipedia.
When the Mori built Honjo is unclear, as is whether there was a keep in Terumoto's time.
The walking time from the foot to the summit, barrier-free access, toilets, English information and photo rules could not be confirmed from official sources.
TT mk2CC BY-SA 3.0Wikimedia Commons
