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

Image: Remains of an Edo-period storehouse

Currently, construction of the Keio Museum Commons (KeMCo) is underway at the foot of the Maboroshi no Mon on the east side of the Mita Campus. 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 overlooked from the Maboroshi no Mon, many people likely noticed it.

Many people might wonder, "Archaeological remains in that location? Why excavate?" However, beneath the ground in areas that were once part of the city of Edo, traces of human activity in the giant city of Edo remain everywhere. In a sense, anywhere that has not been destroyed by development since the modern era can be considered 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, the Minato City Curriculum Advisory Committee conducted a small-scale excavation in December 2017 to confirm whether the site was a protected archaeological site. 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. Since this location is shown as a town area (machiya) on Edo-period maps, the Curriculum Advisory Committee named the site the Mita 2-chome Machiya Site.

Subsequently, a trial excavation was conducted in September 2018 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 laboratory.

As the name of the site suggests, the excavation survey first focused on the Edo-period town area remains. Immediately after the start of the survey, it was discovered that the Edo-period strata were layered more deeply than expected, and we ended up surveying nearly double the number of features anticipated. 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, the artifacts and survey records are scheduled to be organized over the next year or so, so normally they should be discussed after that. However, during this excavation, unexpected features and artifacts were found one after another, attracting attention from many researchers both within Keio and outside. Therefore, I would like to provide an overview, with the caveat 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 unearthed artifacts, it can be inferred that a town area had formed by the late 17th century, and from the 18th century onward, the presence of multiple storehouses suggests that relatively wealthy townspeople lived there. Trash pits where burnt roof tiles were discarded were prominent, offering a glimpse of the frequent fires in the area. There were no building remains other than the storehouses, which are thought to have faced Mita-dori Street, which was narrower than it is today. In any case, I expect that the lifestyle of the town area in the Mita neighborhood will become clearer through the upcoming organization work.

What attracted particular 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 has not yet been completed, 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 attracted attention because several artifacts rare in general settlement sites, such as inkstones called enmenken and green-glazed pottery, were unearthed from inside and around it. 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 of Musashi Province, which has not seen much progress until now.

On the other hand, although the state of preservation was poor, it is thought that there were five or more pit-dwelling remains within the survey area. Some may date back to the end of the Yayoi period (3rd century), and others appear to include those 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 Yayoi to Kofun period settlement sites in lowlands, making this a valuable case that could lead to clarifying the location and structure of settlements during those periods.

In addition to these traces of human activity, the survey confirmed the accumulation of strata that serve as clues to clarifying changes in 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 archaeology and Japanese history research at the Juku, which has a long history, likely never dreamed that such remains lay dormant beneath their feet. As mentioned earlier, specific survey results are scheduled to be reported in 2020 after the organization work. Please look forward to it.