It was built in 1232 and, in spite of its state of disrepair, it has been declared a national Historic Site because it is the sole surviving example of an artificial harbor from the Kamakura period.
Although its component stones have sunk in the sand, its general contour is still clearly visible when the tide is low as a mound about 200m long.
On its northern side there used to be several stone pillars used to moor ships in port call to avoid strong southern winds, but they are now all lost.
The stele, erected by the Kamakuramachi Seinendan (Kamakura Youth Club) in 1924, explains in Japanese the history of the site and its importance.
768 years ago, a priest named Oamidabutsu asked permission for its building and, with the support of Moritsuna, work was started on July 15th and ended on August 9th.