Genko Borui The was a defensive stone wall , 20 kilometres ( 12 mi ) long , constructed along Hakata Bay in Japan in preparation for an attack by Mongol forces of the Yuan Dynasty after the first attack of 1274 . The second attack of 1281 was thwarted by a typhoon , or kamikaze , and the Mongols were forced to withdraw . In the Edo era , some of the stones were reused for the construction of Fukuoka Castle , though Genkō Bōrui has remained intact at several points along the Hakata Bay . It was originally called . It was designated a national historic site on March 30 , 1931 . History . The Mongol invasions of Japan in 1274 and 1281 were major military efforts undertaken by Kublai Khan to conquer Japan . After the failure of the first invasion , the Kamakura shogunate ( Bakufu ) initiated a series of projects in 1275 to prepare for the next invasion , which they felt was imminent . In addition to improving the organization of the samurai of Kyushu , they ordered the construction of a large stone wall and other defensive structures at many potential landing points , including Hakata Bay . A defensive wall was planned and a tax was levied on the samurai , temples , and shrines , of of construction stone per rice field equivalent to one " koku " of rice . Construction began in March 1276 . The planned date of completion for most of the wall was August of the same year , but the deadline differed depending on the strategic importance of given locations . Construction of the defense wall was made by various Kyushu provinces . These provinces continued maintenance on the wall until the early part of the Muromachi period , and by the latter half of the 14th century it had fallen into disrepair . A part of Genkō Bōrui was completed before the second invasion and prevented the enemy from landing immediately . The invaders were forced to anchor their ships at Shikanoshima Island . The battles occurred over several months between several thousand evenly - matched combatants . Takezaki Suenaga of Higo province joined the battles and had artists draw scrolls concerning the Battle of Kōan . This second attack of 1281 was finally thwarted by a typhoon , or kamikaze , and the Mongols were forced to withdraw . Even later , the defense system was continued , and remained intact until 1332 . In the Edo period , most of the stones were used for the construction of Fukuoka Castle . It was designated a national historic site on March 30 , 1931 . Taxation and transformation . At first , battle - ready soldiers were excluded from taxation , but this policy was soon discontinued and each province in Kyushu was taxed . The tax was usually one " sun " ( 3 . 3 cm ) of the wall ' s length per 1 " tan " of rice field ; the weapons were one shield , one flag and 20 arrows per 1 " jo " ( 3 . 314 yards ) of stone wall . The tax was in the form of men who constructed the wall and in the form of the items ( weapons ) , but later the tax was paid in money ; 114 mon per one " cho " of rice field was typical . The taxation continued to the early part of the Muromachi Bakufu . Structure . The Genkō Bōrui was typically high and wide . The western end was in Imazu , Nishiku , Fukuoka and the eastern end in Kashii , Higashiku , Fukuoka , and about long . It was packed with small stones inside , the seaside steep and the landside less steep . Shields and flags were placed on the Genko Borui and stakes were planted in the sea at irregular intervals . Etymology . In articles of the " Fukuoka Nichi Nichi Shimbun " ( " Fukuoka Daily Newspaper " ) between June 12 , 1913 and June 29 , 1913 , Heijiro Nakayama first used the words " Genkō Bōrui " to mean " Mongolian Invasion defense structure " and he contrasted the Genkō Bōrui from conventional stone defense by its high elevation and its design as a sand dike covered with stones ; a structure which would effectively block an invasion attempt . Archaeological excavations . The Genkō Bōrui was excavated at the locations listed below . All locations were along Hakata Bay , within the city of Fukuoka . In 1958 , human bones corresponding to 200 bodies were found in Imazu near the defensive structure , with ceramics considered to have been used by those convened for the construction of the wall .