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English SummariesBulletin of Gunma

Tamped earthen ramparts in medieval castles
-Based on the examples of the Kanto region-
HARA Makoto

The tamped earthen technique is thought to have been devised in the Shang Dynasty in China.
Several examples of this technique have been observed in the recent excavations in Japan.
This technique was also used and preserved in the earthen ramparts of the medieval castle sites in Japan.
Investigations have revealed that the tamped earthen technique of ancient China was widely used in such fortifications as the famous Kohgoishi in the western part of Japan as well as other fortifications densely distributed in the Tohoku region, the North-eastern half of mainland Japan.
Because of its refined quality it is thought to be an imitation by an artisan who had learned the technique in China and adopted the technique in constructions in Japan.
In the investigations of the moats and the ramparts built as the defensive fortresses of the court headquarters at Dazaifu located in Fukuoka Prefecture, they discovered that ancient Chinese techniques were copied and these moats and ramparts have been identified as tamped earthworks.
But the origin of the tamped earthen ramparts observed at the medieval castle sites can not directly be linked with ancient Chinese techniques.
The tamped earthworks which can be clearly identified as in the above description are very few.
The tamped earthen technique developed in ancient China are defined firstly by different soil types and mixed up and rammed down alternately in thin layers, and then secondly that frames of wooden boards are used in building up the earthwork at every stage, and finally it ends up as regular, thin and horizontal layers lengthwise and breadthwise.
When all these points are taken into account few medieval earthen ramparts fit the bill.
Checking the few examples of the ramparts of the medieval castle sites if the wooden boards were used in the construction none of them used these techniques but other things conform to the definition.
Why they did not use wooden boards in China is because they would need to add water to the soil where the climate is dry and the temperature is low, sparse rainfall, and low humidity gives birth to loess.
In Japan high temperatures, frequent rainfalls and high humidity are good conditions for pounding the soil without adding water, thus I will discuss the civil engineering view points.
The tamped earth ramparts without wooden boards like the Japanese medieval castle sites are an example of the techniques adapted to our country's climatical conditions and it might be said that these are a Japanised tamped earth construction based on the ancient Chinese ones.

Key words: Medieval castle sites; Warring States period; Kanto region

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