Nobori-ishigaki was a method of building stone walls adopted to fortify the defense of Japanese castles that were constructed on the Korean peninsula during Hideyoshi TOYOTOMI's Bunroku-Keicho War.
Japanese castles were built on the Korean peninsula during the Bunroku-Keicho War in order to serve as headquarters for the invading daimyo (Japanese feudal lords), and many of these were constructed near to shorelines and rivers in order to secure landing sites for supply ships from Japan. While castle towers were built on small hills or mountains with a good view of the surrounding areas, structures such as soldiers' residences were constructed on flatland near ports: in order to defend the area between the castle towers and soldiers' residences, Japanese style stone walls (ishigaki) were constructed from flatlands to hills and mountains, finally surrounding the main castle. These were nobori-ishigaki.
Although the idea of preventing enemies from invading from mountainsides dates back to at least the Great Wall of China, nobori-ishigaki were localized structures with the purely military objective of protecting combatants. The major style of castles were Hirayamajiro (castles built on a hill in a plain) whereas Kuruwa (walls of a castle) styles included Renkaku style (second compound and third compound surround the main compound at the center), Teikaku style (main compound is placed adjacent to the castle walls, and additional walls are placed surrounding the main compound), and Rinkaku style (the second compound and third compound surround the main compound at the center).
Although after the withdrawal of Japanese forces from the Korean Peninsula, most Japanese castles were destroied, the Republic of Korea has been conducting investigations and research about those castles as valuable ruins that suggest historical relationships between the castle architecture in China, the Korean Peninsula and Japan.
Nobori-ishigaki in Japan
It is said that Yoshiaki KATO who resided at the Angolpo Castle and Yasuharu WAKISAKA and some other Daimyo who came back from the Korean Peninsula adopted the nobori-ishigaki method when constructing and renovating castles, but many castles were demolished after Ikkoku Ichijo Rei (Law of One Castle per Province) or around the Meiji Restoration, and the history of nobori-ishigaki is not fully understood yet; locations in which they were constructed.
Matsuyama Castle (Iyo Province)
When Yoshiaki KATO started the castle construction in 1602, he built the country's largest nobori-ishigaki but the northern part was demolished around the Meiji Restoration for some reasons, and only the southern part has been preserved intact.
When construction by the shogunate began in 1603, it consisted of a nobori-ishigaki which remains preserved in good condition.
When Yasuharu WAKISAKA had major repairs conducted on the stone wall, a nobori-ishigaki was built but this was later demolished as a result of the 'one castle per province' edict issued by the shogunate, and the remaining stone wall ruins are not well-preserved.