Nagare Sakurayama Kofun Group

Nagae Sakurayama Kofun Cluster: Kanagawa's Largest Ancient Keyhole Tombs

Hidden among the forested hills straddling the cities of Zushi and Hayama on the Miura Peninsula, the Nagae Sakurayama Kofun Cluster (長柄桜山古墳群) is a pair of remarkable keyhole-shaped burial mounds dating from the 4th century. Designated as a National Historic Site in 2002, these are the largest surviving kofun in Kanagawa Prefecture and the only known keyhole-shaped tombs on the entire Miura Peninsula. Perched on hilltops overlooking Sagami Bay, with views stretching from Enoshima to Mount Fuji and from Tokyo Bay to the Boso Peninsula, these ancient tombs offer visitors a rare blend of archaeological wonder and breathtaking coastal scenery — all just one hour from central Tokyo.

What Are the Nagae Sakurayama Kofun?

The Nagae Sakurayama Kofun Cluster consists of two large zenpō-kōen-fun (前方後円墳), or keyhole-shaped burial mounds. This distinctive tomb shape, with a circular rear mound and a trapezoidal front section, was reserved for the most powerful rulers and clan leaders during the Kofun period (3rd–6th century CE). The construction of such monumental tombs required enormous manpower and resources, indicating that a powerful clan with close ties to the Yamato court in the Kinai region once held dominion over this strategic coastal area.

Tumulus No. 1 stands at an elevation of approximately 120 meters and has a total length of 91.3 meters. Its rear circular section measures 51 meters in diameter and rises 7 meters high, while the front section extends 39 meters with a width of 31.5 meters. The mound was constructed by first carving out the underlying bedrock, then building up an embankment of approximately 1.5 meters of earth on top. Excavations revealed a burial pit about 7 meters long and 1.6 meters wide in the center of the rear section, where a clay-covered wooden coffin was once placed.

Tumulus No. 2, located approximately 500 meters to the west at an elevation of about 100 meters, has a total length of 88 meters. Unlike Tumulus No. 1, this mound features fukiishi (葺石) — protective stone cladding on its surface. The lower portions used yellow mudstone carried from the nearby coast, while the upper sections were faced with white sandstone transported from the Sagami River or Tama River areas, demonstrating the considerable logistical capabilities of the builders. Both pot-shaped and cylindrical haniwa (terracotta figures) were discovered at both tombs.

A Dramatic Discovery in 1999

One of the most fascinating aspects of the Nagae Sakurayama Kofun is their remarkably recent discovery. Until 1999, no one knew these massive ancient tombs existed. The story begins around 1994, when a local archaeology enthusiast, the late Mr. Yonosuke Tōke, who lived in Hayama, began to suspect that the shape of a hilltop he could see on topographic maps might be a burial mound.

The breakthrough came in March 1999, when a small area of forest on the hilltop was cleared for the construction of a mobile phone transmission tower. During the work, Mr. Tōke discovered fragments of haniwa among the disturbed earth. This discovery prompted an immediate joint investigation by the education committees of Zushi City, Hayama Town, and Kanagawa Prefecture. The investigation confirmed the presence of a large keyhole-shaped tomb approximately 90 meters in length, and construction of the tower was promptly halted.

Shortly after this initial discovery, archaeologists from Kanagawa Prefecture identified a second potential tumulus on a nearby hilltop about 500 meters to the west. A trial excavation in June 1999 confirmed the presence of fukiishi and haniwa fragments, establishing it as a second keyhole-shaped tomb. The discovery of these two monumental burial mounds — the largest of their kind in the prefecture — was a milestone in the archaeological understanding of the Miura Peninsula region.

Why Was It Designated a National Historic Site?

The Nagae Sakurayama Kofun Cluster was designated a National Historic Site on December 19, 2002. Several factors contributed to this recognition of cultural significance.

First, these are the largest surviving keyhole-shaped tombs in Kanagawa Prefecture and the only known examples on the Miura Peninsula. Their scale and form point to the existence of a powerful ruling clan in an area where no such evidence had previously been found, fundamentally reshaping our understanding of the political landscape of the early Kofun period in the Kantō region.

Second, the tombs occupy a strategically significant location. Tumulus No. 1 commands views of Tokyo Bay and the Boso Peninsula to the east, while Tumulus No. 2 overlooks Sagami Bay and Mount Fuji to the west. The site sits near the mouth of the Tagoe River, which in ancient times was an important maritime transportation route. The ancient Tōkaidō highway — the road connecting the Kinai region to the eastern provinces — is believed to have run along this river valley. This location at a crossroads of land and sea routes helps explain the presence of such powerful rulers in this area.

Third, the tombs are remarkably well preserved. Despite residential development in the surrounding areas since the 1960s, the kofun themselves and their immediate natural environment have been protected, retaining rich biodiversity and lush forest cover.

Highlights and What to See

Surrounding Attractions

The area around the Nagae Sakurayama Kofun offers plenty of additional sightseeing opportunities that can easily fill a half or full day.

Roka Memorial Park (蘆花記念公園) — Located at the foot of Tumulus No. 2, this tranquil park is named after Meiji-era novelist Tokutomi Roka, who lived and wrote in the area. The park features walking trails lined with literary monuments, beautiful autumn foliage, and panoramic views of Sagami Bay and Enoshima. The former Zushi City Local History Museum, housed in a Taisho-era villa once owned by the Tokugawa family, is also located within the park grounds.

Tomb of Rokudai Gozen (六代御前の墓) — Near the entrance to Roka Memorial Park, this quiet memorial marks the grave of Rokudai Gozen (Taira no Takakiyo), the great-grandson of the legendary Taira no Kiyomori. His story is one of the most poignant episodes from the fall of the Taira clan at the end of the Heian period.

Zushi Beach (逗子海岸) — A beautiful sandy beach on Sagami Bay, just a short distance from the kofun area. Popular for swimming, SUP, and kayaking in summer, the beach is also a wonderful spot for year-round sunset viewing with Enoshima and Mount Fuji in the background.

Hayama Shiosai Park and Museum (葉山しおさい公園) — Adjacent to the Hayama Imperial Villa, this seaside park features traditional Japanese gardens, tidal pools, and a museum showcasing marine life from Sagami Bay.

Kamakura — The former medieval capital of Japan is located just two train stops north of Zushi, offering access to dozens of historic temples, shrines, and the Great Buddha statue.

Practical Tips for Visitors

The kofun are located on forested hilltops and require a moderate uphill hike to reach. Wear sturdy walking shoes with good grip, as some sections include steep steps and uneven terrain. Bring water and insect repellent, especially in summer. There are no restrooms or vending machines on the hiking trail itself; the nearest public facilities are at Roka Memorial Park and near the Tomb of Rokudai Gozen.

The site is open year-round and free of charge. Spring and autumn are particularly pleasant seasons for visiting, with cherry blossoms and fresh greenery in spring and vibrant autumn colors in late November and December. Clear winter days offer the best views of Mount Fuji from both tumuli.

Signage and information panels at the site are primarily in Japanese, so international visitors may wish to research the site beforehand or bring a translation app. The hiking trail is well marked and easy to follow regardless of language ability.