Arioka Kofun Group: The Valley of Kings in Shikoku
Nestled in the southwestern hills of Zentsuji City, Kagawa Prefecture, the Arioka Kofun Group is a remarkable collection of ancient burial mounds spanning nearly four centuries of Japanese history. Designated as a National Historic Site in 1984, this cluster of six tumuli tells the story of a powerful local clan whose influence endured from the late 3rd century through the early 7th century — a lineage some scholars believe to be the ancestors of Kukai (Kobo Daishi), one of Japan's most revered religious figures.
While many travelers flock to the famous UNESCO-listed kofun of Osaka, the Arioka Kofun Group offers a far more intimate and accessible experience. Here, you can walk directly atop ancient mounds, peer into stone burial chambers adorned with rare wall engravings, and explore a landscape where Japan's ancient past is woven seamlessly into a quiet, modern city.
What Are Kofun?
Kofun are large earthen burial mounds constructed for the ruling elite of ancient Japan during the Kofun period, roughly spanning from the mid-3rd to the late 6th century. The most distinctive type is the keyhole-shaped mound known as zenpō-kōen-fun, featuring a circular rear section and a rectangular frontal extension. These monumental tombs reflect the political hierarchy and sophisticated funerary culture of the era, often containing elaborate grave goods such as weapons, ornaments, and ceremonial objects.
Zentsuji City alone has over 400 identified burial mounds, making it one of the densest concentrations of kofun in the Shikoku region. Among these, the six tumuli of the Arioka Kofun Group stand apart as the successive tombs of chieftains from a single ruling lineage, offering an unparalleled chronological record of power and cultural exchange in ancient Sanuki Province.
Why the Arioka Kofun Group Is Nationally Designated
The Arioka Kofun Group received its designation as a National Historic Site because of several exceptional qualities. First, the six tumuli represent a continuous line of chieftain burials from the late 3rd century to the early 7th century — an unusually complete chronological sequence that allows researchers to trace how local power evolved over nearly 400 years. While many regions in Kagawa Prefecture saw the construction of keyhole-shaped mounds decline after the early Kofun period, the Arioka area continued to produce large-scale tumuli well into the late Kofun period, highlighting the persistent importance of this locality.
Second, the grave goods excavated from these tumuli reveal deep connections between this regional clan and the central Yamato court. Items such as gilt-bronze crowns, silver-inlaid iron swords, and horse trappings indicate that the chieftains buried here were not merely local rulers, but figures of national significance who maintained direct relationships with the imperial government. Third, the cluster includes a rare decorated tomb with line-engraved wall paintings — one of the very few examples of such art found on the island of Shikoku.
The Six Tumuli: A Journey Through Time
Noda-in Kofun (Late 3rd Century)
Perched at an elevation of approximately 405 meters on the slopes of Mount Ōasa, the Noda-in Kofun holds the distinction of being one of the highest-altitude kofun ever constructed in Japan. This 44.5-meter keyhole-shaped mound is the oldest in the Arioka group, dating to the late 3rd century. Its construction technique is particularly fascinating: the rear circular portion is built entirely of stacked stones (a style known as tsumi-ishizuka), while the frontal rectangular portion uses packed earth topped with a layer of stone. Glass beads, iron swords, and haji-ware pottery were excavated from the stone chamber, all bearing characteristics of the late Yayoi period. Rows of ritual jars encircled the mound, predating the later use of haniwa clay figures.
Murusuyama Kofun (Late 4th Century)
Located on the ridge of Mount Murusu at an elevation of 121 meters, this 50-meter keyhole-shaped mound yielded one of Kagawa Prefecture's most important archaeological finds: a ship-shaped stone sarcophagus carved from a single block of andesite quarried at Mount Washinoyama. The sarcophagus features a stone pillow with sculpted magatama earring motifs, suggesting an intimate attention to the comfort and adornment of the deceased even in death. This artifact is now on display at the Zentsuji Civic Hall.
Tsurugamine No. 4 Kofun (Early 5th Century)
Situated at the southwestern end of Tsurugamine ridge at an elevation of 125 meters, this 26-meter keyhole-shaped mound dates to approximately the early 5th century. While not covered by the National Historic Site designation, it serves as an important link in the chronological chain of chieftain burials that defines the Arioka group.
Maruyama Kofun (Mid-5th Century)
Positioned behind Kitamuki Hachiman Shrine, the Maruyama Kofun is the largest tumulus in the group at 54 meters in length. Its rear circular section measures 30 meters in diameter. Although excavated artifacts remain unidentified, evidence of rammed-earth (hanchiku) construction techniques has been confirmed at the constriction between the two mound sections, demonstrating advanced engineering methods.
Ōhakayama Kofun (Mid-6th Century)
The centerpiece of the Arioka group, the Ōhakayama Kofun is a 46-meter keyhole-shaped mound that produced some of the most spectacular grave goods in all of Shikoku. Its side-entry stone chamber contained gilt-bronze crowns — the first of their kind ever discovered in Japan — along with silver-inlaid iron swords, horse trappings, abundant Sue-ware pottery, and personal ornaments. The presence of a stone sarcophagus structure called ishiyakata inside the chamber is particularly noteworthy, as this style is far more commonly associated with Kyushu, suggesting active cultural exchange across the Seto Inland Sea. Today the mound is maintained as a beautifully landscaped archaeological park where visitors can climb to the summit for panoramic views of the city and the five-story pagoda of Zentsuji Temple.
Miyagao Kofun (Late 6th – Early 7th Century)
The youngest tomb in the group, the Miyagao Kofun is a circular mound (empun) approximately 22 meters in diameter, built adjacent to Mitachi Shrine. What makes this tomb exceptional is its decorated stone burial chamber. Line-engraved images on the chamber walls depict warriors, figures on horseback, groups of people, and fleets of ships. These scenes are believed to represent a mogari ceremony — a traditional rite performed between death and formal burial for a person of high rank. Decorated kofun of this type are predominantly found in northern Kyushu, making the Miyagao Kofun exceedingly rare for Shikoku and the Seto Inland Sea region. While the actual chamber is sealed for preservation, a full-scale replica and detailed interpretive panels are available for visitors at the adjacent park.
The Kukai Connection
Zentsuji City is renowned as the birthplace of Kukai (774–835), the founder of Shingon Buddhism and one of the most influential figures in Japanese religious history. Kukai was born into the Saeki clan, a powerful family that had maintained its prominence in this region since the Kofun period. Some researchers have suggested that the chieftains buried in the Arioka Kofun Group may be direct ancestors of the Saeki lineage. While this connection has not been definitively established through archaeology, the proximity of these ancient tombs to Zentsuji Temple — the 75th stop on the famous 88-temple Shikoku Pilgrimage — creates a compelling narrative that links Japan's ancient burial culture with one of its greatest spiritual traditions.
Visiting the Arioka Kofun Group
Three of the six tumuli — Ōhakayama, Miyagao, and Noda-in — have been developed as archaeological parks with interpretive signage and well-maintained paths. The Ōhakayama and Miyagao parks are conveniently located along the Zentsuji-Ōnohara road, just a short drive or moderate walk southwest of central Zentsuji. The Noda-in Kofun requires a more adventurous trip up Mount Ōasa, but rewards visitors with breathtaking mountain scenery and a sense of stepping back into the earliest chapter of Japan's tumulus-building era.
Every year on April 29, Zentsuji City celebrates "Kofun Day," when the normally restricted stone chambers of the Ōhakayama and Miyagao kofun are opened to the public, and the Noda-in mound is also specially accessible. This is the single best day of the year to experience the Arioka Kofun Group in its full splendor.
Artifacts excavated from the kofun are housed at the Zentsuji Municipal Folk Museum, located within the Akamon-suji shopping street near Zentsuji Temple. Admission is free, and the collection includes approximately 1,100 archaeological items on the first floor, with folk cultural materials on the second floor.
Surrounding Attractions
Zentsuji City offers a rich array of experiences beyond its ancient tombs. Zentsuji Temple (Temple No. 75 on the Shikoku Pilgrimage) is the city's spiritual heart, founded in 813 on the very site where Kukai was born. The temple complex features an impressive five-story pagoda and the atmospheric underground passage known as Kaidan-meguri, where pilgrims walk in complete darkness beneath the main hall.
The Former Zentsuji Kaikōsha, a Meiji-era officers' club building designated as a National Important Cultural Property, offers a glimpse into the city's modern military history. For nature lovers, Mount Ōasa provides hiking trails through dense forest with panoramic views of the Sanuki Plain and the Seto Inland Sea. The nearby town of Kotohira, home to the famous Konpira-san shrine with its 1,368 stone steps, is just one train stop away.
Kagawa Prefecture is also celebrated as the udon capital of Japan. Zentsuji and its surroundings are dotted with beloved udon noodle shops where visitors can enjoy fresh, handmade Sanuki udon at remarkably affordable prices.
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Q＆A
- Can I enter the stone burial chambers of the kofun?
- The stone chambers are normally sealed for preservation. However, every year on April 29 (Zentsuji City's "Kofun Day"), the chambers of Ōhakayama Kofun and Miyagao Kofun are opened for public viewing, and the Noda-in Kofun mound is also specially accessible. A full-scale replica of the Miyagao Kofun chamber is available year-round at the adjacent park.
- Is there an admission fee to visit the kofun?
- No. The archaeological parks at Ōhakayama, Miyagao, and Noda-in kofun are open to the public free of charge. The Zentsuji Municipal Folk Museum, which displays excavated artifacts, is also free of charge.
- How do I get to the Arioka Kofun Group?
- The closest station is JR Zentsuji Station on the Dosan Line. From there, the Ōhakayama and Miyagao kofun parks are about a 5-minute drive or 20-minute walk to the southwest. By car, take the Takamatsu Expressway to Zentsuji IC, then approximately 10 minutes by local road. Parking is available at the kofun parks.
- Are there English-language signs or guides available?
- Interpretive signage at the archaeological parks is primarily in Japanese, though some information panels include brief English explanations. The Zentsuji Municipal Folk Museum may have limited English materials. Visitors are recommended to research the site in advance or use a translation app for the fullest experience.
- What is the best season to visit?
- The kofun parks can be enjoyed year-round, but spring (especially late April for Kofun Day on April 29) and autumn are particularly pleasant. The cherry blossom season in late March to early April adds beautiful color to the landscape around the tumuli. Summer visits to the Noda-in Kofun on Mount Ōasa offer cooler mountain air, though be prepared for a steep hike.
Basic Information
| Official Name | Arioka Kofun Group (有岡古墳群) |
|---|---|
| Designation | National Historic Site (designated November 29, 1984) |
| Location | Zentsuji-chō and Ikuno-chō, Zentsuji City, Kagawa Prefecture |
| Component Tumuli | Noda-in Kofun, Murusuyama Kofun, Tsurugamine No. 4 Kofun, Maruyama Kofun, Ōhakayama Kofun, Miyagao Kofun (6 tumuli total) |
| Period | Late 3rd century – early 7th century (Kofun period) |
| Admission | Free |
| Special Opening | April 29 each year ("Kofun Day") — stone chambers opened to public |
| Museum | Zentsuji Municipal Folk Museum (善通寺市立郷土館), free admission, open Tue/Wed/Fri/Sat/Sun 10:00–16:00 |
| Access | JR Dosan Line, Zentsuji Station — approx. 5 min by car or 20 min walk to Ōhakayama Kofun. Takamatsu Expressway, Zentsuji IC — approx. 10 min by car. |
| Managing Body | Zentsuji City |
References
- National Designated Historic Site: Arioka Kofun Group — Zentsuji City Official Website
- https://www.city.zentsuji.kagawa.jp/soshiki/50/ariokaindex.html
- Arioka Kofun Cluster — Wikipedia (English)
- https://en.wikipedia.org/wiki/Arioka_Kofun_Cluster
- Ōhakayama Kofun (Zentsuji City) — Wikipedia (Japanese)
- https://ja.wikipedia.org/wiki/%E7%8E%8B%E5%A2%93%E5%B1%B1%E5%8F%A4%E5%A2%B3_(%E5%96%84%E9%80%9A%E5%AF%BA%E5%B8%82)
- Arioka Kofun Group — Cultural Heritage Online (bunka.nii.ac.jp)
- https://bunka.nii.ac.jp/heritages/detail/202756
- Arioka Kofun Group — Kotobank Encyclopedia
- https://kotobank.jp/word/%E6%9C%89%E5%B2%A1%E5%8F%A4%E5%A2%B3%E7%BE%A4-1443166
- Ōhakayama Kofun (Arioka Kofun Group) — Tabi-mag.jp
- https://tabi-mag.jp/ka0043/
- Five Things to Do in Zentsuji City — Kukai NAVI (Zentsuji Tourism Association)
- https://www.kukainavi.com/en/point/003.html
- Zentsuji Municipal Folk Museum — Zentsuji City Official Website
- https://www.city.zentsuji.kagawa.jp/soshiki/50/kyoudokan.html
Last verified: 2026.03.09