Akibayama Kofun Cluster: Early Burial Mounds of Ebina, Japan
Site at a Glance
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- Country
- Japan
- Primary era
- Classical
- External website
- Open
- Eras represented
- Classical
- Civilizations
- Yamato
- Site type
- Burial
- Remains
- Necropolis
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History
Akibayama Kofun Cluster is a group of Kofun-period burial mounds in Ebina, Japan, built by powerful local chiefs between the third and fourth centuries. The Kofun period was the era from roughly the third to sixth centuries when monumental Japanese burial mounds were constructed. The cluster occupies a ridge of the Zama Hills overlooking the Sagami River basin and is regarded as one of the oldest kofun groups in eastern Japan.
Origins and early development
The earliest mounds at Akibayama belong to the period when kofun society was taking shape. Kofun No. 3 and Kofun No. 4 were built in the third century, followed by Kofun No. 2 in the late third or early fourth century. Kofun Nos. 1 and 5 probably date from the fourth century and represent the final construction phase. The sequence moves from irregular and varied forms toward more standardized keyhole-shaped mounds, showing a local adaptation of changing burial traditions.
Kofun No. 3 is considered one of the earliest keyhole-shaped burial mounds in eastern Japan. A keyhole-shaped mound has a circular rear section joined to a projecting front section. No. 3 was a transitional monument between Yayoi-period burial mounds and early kofun. The Yayoi period preceded the Kofun period and was associated with settled agriculture, regional communities, and rectangular burial mounds surrounded by moats. The larger scale of No. 3, compared with the square moated burial mounds then common around Sagami Bay, reflects the emergence of a local leader with connections to the Yamato polity, the early centralizing authority based in the Kinai region.
The people buried at Akibayama are interpreted as chiefly figures who exercised substantial influence over communities in the Sagami River basin. The cluster’s location near the river and a route toward Musashi, broadly associated with the course of present-day National Route 246, connected the mounds with local production and settlement centers and an important transport corridor. Their construction traditions indicate regional power, while the earth-built mounds and their comparatively limited external fittings have been taken to suggest a lower position within the wider Yamato political order than that of the most elaborately equipped chiefly tombs.
Ritual practices and regional connections
Kofun No. 2 preserves evidence of a funerary rite involving fire. Pottery, including cylindrical vessels, was deliberately broken and scattered after being exposed to heat. The reason for the widespread breakage remains uncertain. Some vessels carried mercury vermilion, a red mercury-sulfide pigment commonly associated with ritual use in early burial contexts. Charcoal from the mound produced an AMS radiocarbon date of approximately AD 250–325, using a method that estimates the age of organic material from very small quantities of carbon isotopes.
The pottery from No. 2 includes local Sagami vessels alongside pieces thought to have arrived from the Tokai and Kansai regions. Four unusual cylindrical vessels are linked to Late Yayoi special stands from the Okayama area and may represent an early stage in the development of cylindrical haniwa, the clay objects later placed around or on burial mounds. These finds point to contacts extending beyond the immediate Sagami region.
The cluster’s construction ended after the fourth century. The reason is uncertain. Nearby chiefly lineages may have disappeared, or restrictions on the construction of large burial mounds may have been introduced. The later Kamihamada Kofun Cluster in Ebina, including Hiyotan-zuka Kofun, may have had a connection with Akibayama, since fragments from Hiyotan-zuka resemble cylindrical pottery excavated from Kofun No. 2.
Recognition and archaeological investigation
The name Akibayama comes from an Akiba Shrine that formerly stood on the summit of Kofun No. 2. The shrine was associated with protection from fire, and the mound was known as Akibayama before the name came to designate the whole cluster. The group was known by the late Meiji period, while records from the Meiji and Taisho periods preserve information about mounds that later vanished and about a front section once present on Kofun No. 3.
A mound survey took place in 1969, followed by twelve archaeological excavations between 1987 and 2003. A pre-development investigation in 1988 suggested that Akibayama might be among the oldest kofun groups in Kanagawa Prefecture. Parts of the moats around Kofun Nos. 3 and 5 were destroyed after that investigation and before heritage protection was secured. The cluster was designated a National Historic Site on July 14, 2005, and Kofun No. 6 was added to the designation in 2006.
Six mounds are confirmed along the ridge, although urban development, especially residential construction beginning in the mid-1960s, altered the archaeological landscape. A possible continuation into Zama City remains unconfirmed. The mound areas have been investigated except for No. 6, while the burial facilities themselves have not been excavated. The cluster therefore remains important both for its surviving monuments and for the evidence its sequence provides about the emergence of kofun society around Sagami Bay and in southern Kanto.
Remains
Ridge layout and construction
The six mounds follow the ridge from southeast to northwest in the order Nos. 1, 2, 3, 5, 4, and 6. Nos. 1 through 4 stand within about 50 meters of one another, while No. 6 is approximately 250 meters north of No. 4. The ridge lies roughly 75–80 meters above sea level, and the summit of No. 2 reaches 84.6 meters, the highest point in Ebina City. The mounds were formed by cutting into the Fuji black soil and Kanto Loam of the Zama Hills, then adding earth to build up the burial forms. Their construction generally uses earthen slopes without stone facings, stepped sides, or cylindrical haniwa.
The confirmed forms include three front-circular/rear-circular mounds, one front-square/rear-square mound, and one square mound. The three front-circular/rear-circular examples include one regular keyhole-shaped mound and two early or nonstandard forms. This range of designs preserves the changing relationship between older Yayoi burial traditions and the developing forms of early kofun.
Front-circular and rear-circular mounds
Kofun No. 1
Kofun No. 1 is a regular keyhole-shaped mound approximately 59 meters long. Its rear circular section is 33 meters in diameter and 6.3 meters high, while its front section measures 26 meters in length and 2.8 meters in height. A groove was cut directly in front of the front section, forming part of the mound’s external arrangement. Small round-bottomed pottery and iron arrowheads were excavated from the mound. The pottery resembles material distributed widely across Japan, rather than the more locally focused assemblages associated with Nos. 2 and 3.
Kofun No. 2
Kofun No. 2 measures approximately 50.5 meters from end to end. Its rear circular section is 33 meters across and 7.7 meters high, while the front section is 17.5 meters long and 4.6 meters high. The short front section and unusually tall profile give it an early, nonstandard appearance, although it shares important features with No. 3. A groove lies directly before the front section.
Local Sagami pottery occurs with vessels thought to have come from the Tokai and Kansai regions. Some pieces bear mercury vermilion, and four unusual cylindrical vessels resemble forms influenced by Late Yayoi special stands from the Okayama area. Hearth traces and carbonized material were found in the constricted area between the two sections and in part of the front section. The deliberately broken pottery and the heating of the cylindrical vessels after breakage provide physical evidence for the fire-based funerary ritual associated with the mound.
Kofun No. 3
Kofun No. 3 consisted of an irregular rear circular section joined to a small front section. The front section was removed during the twentieth century, but earlier records allow the total length to be estimated at about 51 meters. The surviving rear section measured approximately 38–40 meters across and stood about 7.7 meters high. It was more irregular and proportionally larger than the rear section of No. 2, and a moat surrounded the mound.
A grave pit measuring approximately 9 by 6–7 meters is inferred beneath the summit of the rear section. The burial facility within the pit remains unexcavated. Above it, pottery associated with burial rites included vessels bearing mercury vermilion and large jars, while a concentration of stones suggests that stones may once have been arranged over the grave. Locally developed Late Yayoi jars from Sagami and raised-foot vessels that spread from the Ise Bay coast occur among the finds. Together with the abbreviated keyhole form, these features preserve elements of early kofun and Yayoi burial practice.
Square and front-square/rear-square mounds
Kofun No. 4
Kofun No. 4 is a front-square/rear-square mound made from two joined rectangular sections. It measures 37.5 meters overall. The front section is 12.7 meters long and 2.8 meters high, while the rear section measures 24.8 meters in length and 5.3 meters in height. A moat surrounds the rear section and probably did not continue around part of the front section.
Only a small number of jar fragments were recovered, but their style is considered among the oldest pottery in the cluster. The mound is generally low and, unlike Nos. 1–3, was not formed primarily by cutting deeply into the natural ground and raising a substantial mass of earth. Its rectangular, moated form resembles Yayoi-period burial mounds, although its dimensions are larger.
Kofun No. 5
Kofun No. 5 is a square mound with sides measuring approximately 20 meters and a height of about 5.4 meters. A moat approximately 4 meters wide and 1 meter deep surrounds all four sides. Excavations recovered small round-bottomed pottery and stands dating to the fourth century, placing the mound within the final phase of construction at Akibayama.
Kofun No. 6
Kofun No. 6 lies approximately 250 meters north of No. 4. Detailed investigation has not yet established its form, dimensions, associated features, or archaeological contents. It was included in the National Historic Site designation in 2006.
