Regarding the Excavation Survey at the Construction Site of the Keio Museum Commons (KeMCo)

2019/11/23

Image: Remains of an Edo-period storehouse

Currently, construction of the Keio Museum Commons (KeMCo) is underway on the east side of the Mita Campus, below the Maboroshi no Mon. In fact, for four months from December 2018 to March 2019, before this construction began, an archaeological excavation survey was conducted here. Since the site could be seen from the Maboroshi no Mon, many people likely noticed it.

Many people might wonder, "Were there ruins in that location?" or "Why conduct an excavation?" However, beneath the ground of areas that were once part of the city of Edo, traces of human activity in the giant city of Edo remain everywhere. As long as they have not been destroyed by development since the modern era, in a sense, anywhere can be an Edo-period archaeological site.

Furthermore, in Japan, many such sites are protected as "buried cultural property sites" based on a legal system centered on the Law for the Protection of Cultural Properties. In Tokyo, sites from the Edo period and earlier are subject to protection. If a site must be destroyed due to construction or other reasons, the party responsible for the construction is required to conduct an excavation survey in advance at their own expense. In exchange for the loss of the site, records and artifacts are preserved.

First, following the decision to build KeMCo, in December 2017, the Minato City Curriculum Advisory Committee conducted a small-scale excavation to confirm whether the site was a protected archaeological area. As a result, it was found that strata containing Edo-period artifacts remained in good condition, and it was decided to conduct a full-scale excavation survey before construction. Additionally, since this location was shown as a merchant house (machiya) on Edo-period maps, the Curriculum Advisory Committee named the site the Mita 2-chome Machiya Site.

Subsequently, in September 2018, a trial excavation was conducted to estimate the duration and cost of the excavation. Based on those results, a full-scale excavation survey was scheduled for approximately four months starting December 3. The survey was commissioned to Kyowa Kaihatsu Co., Ltd. under the guidance of the Minato City Curriculum Advisory Committee and the Archaeology and Ethnology.

As the site name suggests, the excavation survey first proceeded with a focus on the Edo-period merchant house remains. Immediately after the survey began, it was discovered that the Edo-period strata were layered more deeply than expected, and we ended up investigating nearly double the predicted number of features. Furthermore, from around the middle of the survey period, a series of unexpected features from the Heian period and earlier began to be discovered beneath the Edo-period strata. Due to these repeated unforeseen circumstances, there were concerns about completing the survey within the timeframe, but thanks to the efforts and cooperation of those involved, we managed to finish just before the start of construction.

Regarding the results of the excavation, since the excavated artifacts and survey records are to be organized over the next year or so, they should properly be discussed after that. Nonetheless, this excavation led to the discovery of one unexpected feature and artifact after another, attracting attention from many researchers both within Keio and beyond. Therefore, I would like to provide an overview, with the disclaimer that these are findings as of the present moment.

First, regarding the Edo period, over 300 features such as building remains, cellars, and trash pits were detected, and artifacts filling more than 100 containers were unearthed. From the excavated artifacts, it can be inferred that a merchant district had formed by the late 17th century. From the 18th century onward, the presence of multiple earthen storehouses (dozo) suggests that relatively wealthy townspeople lived there. Trash pits where burnt roof tiles were discarded were prominent, offering a glimpse into the frequent fires in the area. There were no building remains other than the storehouses, which suggests they likely faced Mita-dori Street, which was narrower than it is today. In any case, I expect that through the upcoming organization work, a part of the merchant life in the Mita neighborhood will be clarified.

What particularly attracted attention in this excavation were the features and artifacts from the Heian period and earlier. As the analysis of the timing of the features and their mutual relationships is currently incomplete, I will introduce them here for convenience by dividing them into ancient ditches and pit-dwelling remains from the Yayoi to Kofun periods.

The ditch was relatively large, over 3 meters wide, and extended linearly toward Mita-dori Street. It is thought to be a boundary ditch for some kind of facility or a road. This ditch drew attention because several artifacts rare in general settlement sites were unearthed from inside and outside the ditch, such as inkstones called enmenken (circular inkstones) and Ryokuyu (green-glazed) pottery. These are often found at government offices (kanga) or temples, and this was the first discovery of its kind in Minato City. The nature of the facility equipped with this ditch will be carefully examined in the future, but there is no doubt that these results will challenge existing research on the local administrative and transportation systems of the Ebara District in ancient Musashi Province, which has not progressed much until now.

On the other hand, although the pit-dwelling remains were in poor condition, it is thought that five or more existed within the survey area. Some may date back to the end of the Yayoi period (3rd century), and others appear to include remains from the early Kofun period (4th century) and the end of the Kofun period (7th century). In the southern Kanto region, there are few examples of surveys of settlement sites from the Yayoi to Kofun periods in lowlands, making this a valuable case that could lead to the elucidation of the location and structure of settlements during those periods.

In addition to the traces of human activity mentioned above, the survey confirmed the accumulation of strata that serve as clues to clarifying the transition of topography and environment over tens of thousands of years, and samples were collected for analysis.

Above, I have briefly introduced the excavation survey within the KeMCo construction site. Even the predecessors of Juku's archaeology and Japanese history research, which has a long history, likely never dreamed that such ruins lay dormant beneath their feet. As mentioned earlier, the specific survey results are scheduled to be reported in 2020 after the organization work. Please look forward to it.