Genko Borui (元寇防塁) at Nagahama Beach

We stopped at Genko Borui at Nagahama Beach (長浜海水浴場), located in Imazu (今津), Nishi-ku, Fukuoka before going to Futamigaura Beach.

=Summary=
The Genkō Bōrui (元寇防塁, Genkō Bōrui^?) was a defensive stone wall, 20 kilometers (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.^[1] 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 "Ishitsuiji" (石築地^?). It was designated a national historic site on March 30, 1931.
From Wikipedia