Isshōmasu Site: A Medieval Ridge Fortification in Kamakura, Japan
Site at a Glance
- Rating
- 3.6
- Popularity
- Very Low
- Country
- Japan
- Primary era
- Medieval
- External website
- Open
- Eras represented
- Medieval
- Civilizations
- Ashikaga shogunate, Kamakura shogunate
- Site type
- Military
- Remains
- Fort
On this page6 sections
History
Isshōmasu Site is an archaeological site and former mountain fortification in Kamakura, Japan, on a ridge between the Gokuraku-ji district and the Daibutsu Pass. Its construction date and original function remain uncertain, but Kamakura City and the Agency for Cultural Affairs interpret it as a defensive work from the late thirteenth to early fourteenth century, during the later Kamakura and early Nanbokuchō periods. The Kamakura period was the era of Japan’s first warrior government, while the Nanbokuchō period was marked by rivalry between competing imperial courts.
Origins and changing interpretations
Isshōmasu is thought to have monitored and defended a transportation route across the ridge. A different interpretation places its construction in the fifteenth century, possibly during the Eikyō War of 1438 or the early phase of the Kyōtoku War, a series of conflicts in the Kantō that began in 1455 and continued into the late fifteenth century. The earthwork’s lack of a surrounding outer ditch and the relatively gentle slope of its exterior face have led one castle specialist to question whether it was originally a castle. It may instead have begun as a temple or another non-military site that was temporarily fortified.
Archaeological investigation and protection
The Kanagawa Prefectural Board of Education and Kamakura Municipal Board of Education carried out a distribution survey and archaeological excavation in 2000. Twelve trenches were investigated at Isshōmasu and in its surrounding area. The site was designated a National Historic Site of Japan on February 6, 2007.
Another defensive installation, the Gongōmasu Site, lies approximately 700 metres southeast on a hillside behind a temple. It forms part of the nationally designated Buppōji Temple Site. Gongōmasu, like Isshōmasu, is considered to have served a defensive purpose from the mid-thirteenth to early fourteenth century. From around the late fourteenth century, it was apparently converted into a place of memorial worship associated with stone monuments.
Remains
Isshōmasu occupies a ridge on a hill approximately 90 metres above sea level, with the central area at an elevation of 94 metres and steep slopes around it. The remains are arranged as a single-compartment fortification enclosed by a roughly rectangular earthwork. Inside is a trapezoidal level area measuring approximately 32.5 metres along the east side, 35 metres along the west side, 27.5 metres along the south side, and 18 metres along the north side.
Earthwork enclosure
The surrounding earthwork is approximately 1.5 to 2.8 metres high and 5 to 8 metres wide. A gap about 3.5 metres wide at the southwest corner is interpreted as the entrance. Narrow, flat subsidiary areas follow the east and west sides, forming routes along the ridge. A cross-ridge ditch, a defensive trench cut across elevated ground, is approximately 6 metres wide and separates the summit from a square-shaped level area to the north.
Construction and archaeological finds
The northern earthwork was made by cutting and shaping the ground, while the southern section consists of piled mudstone blocks. At least two further episodes of piling were identified. Excavated material included fragments of late-thirteenth-century Ko-Seto grater dishes, a medieval ceramic tradition associated with Seto, together with unglazed earthenware dishes and Tokoname jars. The northern ditch also produced late-thirteenth-century unglazed dishes and Tokoname jar fragments, as well as pieces of a fourteenth-century Chinese qingbai-ware meiping vase, a pear-shaped vessel with a pale blue-green glaze.
