Excavations are underway at the Historic Site of the Bitchu Kokubun-niji Temple Ruins in Kanbayashi, Soja City.
The area stretching from the right bank of the Ashimori River in northwestern Okayama City and around Tsukuriyama Kofun to Soja City is known as Kibiji. The five-story pagoda of Bichu Kokubun-ji Temple is a symbol of Kibiji.
In one part of this area, the remains of Bichu Kokubun-niji Temple, said to have been built in the 8th century, still stand. However, the full picture has remained shrouded in mystery.
Since fiscal 2023, excavations by the Okayama Prefectural Ancient Kibi Cultural Properties Center have been underway, and an on-site briefing session was held.
The information presented was current when this article was published in February 2024. Please note that it may differ from current information.
Establishment of Bichu Kokubun-niji Temple
During the Tenpyo era at the beginning of the Nara period, droughts, earthquakes, and other natural disasters continued, heightening social unrest.
Emperor Shomu decided to pacify the nation through Buddhism and resolved, among other things, to build a Great Buddha in Nara.
Under this philosophy, known as protecting the nation through Buddhism, an edict to establish provincial monasteries and nunneries was also issued. This was in 741.
The edict called for a monastery and a nunnery to be built as a pair in each of the more than 60 provinces across the country.
In Bitchu Province, it was decided that a monastery would be built to the west and a nunnery to the east, with Komorizuka Kofun between them, in what is now Kanbayashi, Soja City.
In the Nara period, Japan had more than 60 provinces, such as Bizen Province and Bitchu Province, corresponding to today's prefectures.
Komorizuka Kofun was built in the 6th century.
Historic Site of the Bitchu Kokubun-niji Temple Ruins
Although the monastery and nunnery were established in this way, little is known about what happened afterward.
The present-day Bichu Kokubun-ji Temple was built on the site of the provincial monastery during the Edo period, and is different from the Nara-period temple. Meanwhile, it is thought that the site of Bichu Kokubun-niji Temple was never reused and has remained so to this day.
No detailed investigations have been conducted at the Bitchu Kokubun-niji Temple ruins to date. The on-site information board shows a reconstruction of the temple based on features such as the foundation stones of the main hall, still exposed today, and the remains of an earthen wall called a tsuiji that surrounded the entire temple.
The area enclosed by the tsuiji measured 108 meters east to west and 216 meters north to south.
Okayama Prefectural Ancient Kibi Cultural Properties Center
The excavations are being conducted by the Okayama Prefectural Ancient Kibi Cultural Properties Center.
The center is a prefectural institution whose purpose is to investigate, research, preserve, and make use of buried cultural properties in Okayama Prefecture.
Since 2020, it has been carrying out the “Kibiji Historical Heritage” Promotion Project, and the investigation of the Bitchu Kokubun-niji Temple ruins is part of that effort.
I hope to introduce this promotion project in more detail on another occasion.
On-site briefing session check-in
Many participants had gathered at the north prefectural parking lot of Kibiji Fudoki-no-Oka, the meeting and check-in point.
A total of 120 people attended the three briefing sessions, making for a very lively event.
In addition, the site remained open to the public for the week following the briefing sessions. More than 200 people reportedly visited, showing the high level of interest.
The Bitchu Kokubun-niji Temple ruins are about 500 meters east of the parking lot. We walked past Bichu Kokubun-ji Temple and Komorizuka Kofun, following the signs.
Excavation site
The fiscal 2023 excavations focused on three locations: the South Gate, Middle Gate, and Lecture Hall.
Here is an introduction to what was explained at each location.
South Gate
The South Gate was the temple's main entrance.
On top of levelled ground, a raised platform was built using a construction method called hanchiku. It is thought that gate pillars set on foundation stones supported a tiled roof.
The investigation confirmed the platform, a ditch, and traces of the earthen wall.
Let's overlay the on-site explanation on the photograph.
The photograph was taken at the spot where the western edge of the platform was identified.
The top surface of the platform that was uncovered is in the left foreground, and the cut cross-section can be seen farther back.
Later soil layers, including earth from the collapse of the earthen wall, lie on top of the platform. The large depression at the lower right is thought to be a ditch.
The cross-section beneath the platform shows that the natural ground was levelled, and a sturdy platform was built above it by compacting layers of earth using the hanchiku method.
Let's also look at a foundation stone excavated at the South Gate.
On top of the layer of levelling soil, packing stones to stabilize the foundation stone were placed.
The upper surface of the foundation stones placed on top appears to align with the upper surface of the platform built using rammed earth.
The structure of the South Gate has been determined in this way, and the platform is estimated to measure 12 m east to west and 9 m north to south.
The earthen wall was reportedly as much as 3.5 m high.
Middle Gate
The Middle Gate was an entrance for accessing the corridor leading to the Main Hall.
A platform was also confirmed here. An earthen rampart was connected to it, and measured 20 m east to west and 4 m north to south.
Foundation stones were also expected to be found, but none were unearthed.
Instead, traces thought to be postholes were discovered. The Middle Gate is believed to have been built using the post-in-ground constructionmethod, without foundation stones.
Perhaps it was a relatively small gate, and the roof was not particularly heavy.
Lecture Hall
The Lecture Hall was a building where nuns studied.
Two foundation stones remain exposed at the west end even today.
Excavation of the Lecture Hall is ongoing. The platform’s dimensions have only just been determined: 28 m east to west and 20 m north to south.
A stone that may be a foundation stone had also been found at the east end.
The investigation of the Lecture Hall reportedly yielded some interesting discoveries. One was that pottery dating to around the 10th century was found in a spot where a foundation stone had been removed.
Also, iron implements were unearthed and burnt earth was confirmed.
This may indicate that the Lecture Hall had already been lost by the Heian period, relatively soon after the temple was established.
It is also thought that the site may have been used as a blacksmithing workshop.
From the Writer
Since 2020, the Okayama Prefectural Ancient Kibi Cultural Properties Center has been promoting the “Kibiji Historical Heritage” Appeal Promotion Project.
Excavations at the Historic Site of Bichu Kokubun-niji Temple began in 2023.
The Historic Site of Bichu Kokubun-niji Temple had until now been shrouded in mystery, but this investigation is gradually revealing the locations, dimensions, and structures of the South Gate, Middle Gate, and Lecture Hall.
However, the information and figures presented here are preliminary and may change as further investigations are conducted.
We look forward to investigations of the Main Hall and other structures planned for 2024 and beyond.
I look forward to seeing the findings introduced as part of the Appeal Promotion Project.
When visiting the five-story pagoda at Bichu Kokubun-ji Temple, a symbol of Kibiji, why not also visit the nearby Historic Site of Bichu Kokubun-niji Temple, a little to the east? You may hear the whispers of the nuns.
On-Site Briefing at the Historic Site of Bichu Kokubun-niji Temple Information
| Name | On-site briefing at the Historic Site of Bichu Kokubun-niji Temple |
|---|---|
| Date | On-site briefing January 27, 2024 Session 1: 10:00–11:00 a.m., Session 2: 1:00–2:00 p.m., Session 3: 3:00–4:00 p.m. Site open to the public January 29–February 2, 2024 10:00 a.m.–12:00 p.m., 1:00–3:00 p.m. |
| Location | Excavation site at the Historic Site of Bichu Kokubun-niji Temple, Kamibayashi, Soja City |
| Admission (tax included) | Free |
| Website | Okayama Prefectural Ancient Kibi Cultural Properties Center |
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