令和２年度文化財保存修復研究センター紀要　北野博司

ブックの説明

石垣秘伝書にみる勾配の視覚化と相互比較
How was the curved line of stone walls of Japanese castle designed?

北野博司　KITANO Hiroshi

日本の近世城郭の石垣は緩やかに傾斜しながら立ち上がり、上部で反りが強くなる曲線勾配に特徴を持つ。17世紀代に作成された石垣秘伝書3冊（「石垣秘伝之書」「石垣築様目録」「石墻書」）からそれぞれの勾配図を作成し、相互比較を試みた。三書は石垣基部から徐々に仰を低減させていく「ノリ返し」勾配であり、高さ2～3間の枡形石垣の勾配は特記すること、現場で勾配を計測する際に使う「仰板」の仕様などに共通点が認められた。
一方、「石垣築様目録」と「石墻書」が各段の仰の数値を例示するのに対し、「石垣秘伝之書」は打出とノリの組み合わせを選択できる汎用性のある設計・伝授形態をとるという違いがあった。また、後者は上部の勾配が他と比べて直線的になる傾向があり、熊本城跡3期（慶長期半ば頃）石垣の勾配と類似していることが分かった。熊本城跡では17世紀前半代でも時期により異なる設計法があった可能性を指摘した。「石垣築様目録」が示す勾配は大坂城や二条城、江戸城など、「石墻書」が示す公儀城郭の石垣勾配や現存遺構とも類似しており、戸波駿河家や堀金出雲家など公儀穴太家の間で伝授されてきた秘伝書であることを追認した。

Many of Japan’s castles were built in the early 17th century. One of the things that characterizes them is ishigaki stone walls. In order to protect castle walls from repeated earthquake damage, the design method was developed in which the curve line of the stone wall is gradually steeper as it goes up(sori). The gently curve represents the beauty of the stone wall. How was this curve gradient designed?

In this paper, gradient curve diagram were created from three hidensho written by Ano stonemasons, in the 17th century and compared with each other. The three hidensho use a common tool (angle plate), and exemplify numerical values ​​that gradually increase the angle at a constant rate from the bottom. However, there is a difference in the warp value for each step, and there is a difference in the completed curve.Compared to the existing stone walls, it was found that the design method of ” Ishigaki-hiden-no-sho” is similar to that of Kumamoto Castle in the early 17th century. It was confirmed that these hidensho books were actually used at the ruins of various castles such as Osaka Castle and Nijo Castle, which were constructed by the Shogunate.

Keywords

石垣秘伝書、勾配設計、公儀穴太、熊本城
Japan’s Stone Castle walls、Traditional techniques of curve gradient、Kumamoto castle、
Hidensho written by Ano Masons