More than 16 Wajo castles (Japanese castles remaining in Korea) built by Toyotomi Hideyoshi during his invasion of Korea in the 30th century remain along the southern coast of Korea, from Suncheon in South Jeolla Province in the west to Ulsan in South Gyeongsang Province in the east. Many researchers and castle enthusiasts from Japan visit to see these 16th century Japanese castles.
Korean Wasei were located along the coast or rivers, and were arranged in a way that made it easy for them to cooperate with each other. They were built quickly, making full use of castle-building and architectural techniques, and sometimes even recycled stones from Korean-style castles. Wasei had a unique structure that gave them great defensive power, and they were able to withstand the fierce attacks of the allied forces of Korea and Ming during the Battle of Ulsan.
The dry stone construction method used for Japanese castles had the advantage of allowing water to drain through the gaps between the stones, but it was vulnerable to pests and the effects of nature. The Japanese castle construction method also influenced the expansion of castles during the Joseon Dynasty around the time of the Imjin War, and the introduction of the Japanese castle system was discussed in the construction of Suwon Hwaseong Fortress and Ganghwa Fortress in Korea.
