Defense Walls Against Mongol Invasions (Genko Borui)   A defense wall was constructed for roughly 20 kilometers along the coastline of Hakata Bay more than 7 centuries ago to meet any invasion plans by the Mongols. Together with the two typhoons, this stone defense wall, which was called ((gIshitsuiji)) hin those days, smashed the bold ambition of the Mongols. The walls had several different combinations of materials and structure. Completing such a project in merely half a year is remarkable. How were the defense walls built? After the first Mongol invasion failed, a stone defense wall was built by order of the Kamakura shogunate in preparation for the next invasion. Each vassal in the Kyushu region was instructed to build a length of the stone structure based upon the size of his landholding. The completed stone wall extended roughly 20 km from Imazu to Kashii and was constructed in just six months. Since construction of the wall was completed so quickly, it must have been done by the various vassals simultaneously. The ruins indicate different styles of construction depending on the vassal to whom the section was assigned, although all sections had a common front stone wall facing the sea. The Imazu area section allocated to the vassals holding the fief of Osumi (southern Kyushu) and Hyuga (southwestern Kyushu) provinces was a very sturdy structure with a second stone wall to the rear with stone material filling in between. The Iki-no-Matsubara area section built by the vassal holding the fief of Higo province (central Kyushu), however, consisted of a single stone wall on the front side only. The structure of the Nishijin (Momochi) section, whose designee is unknown, had the foundation work in clay, upon which stone walls were built on both sides and filled with clay and sand, thus economizing on stone materials.   (C) Seinan Gakuin University