The Mizuki (an ancient water fortress in Fukuoka Prefecture) (水城)
The Mizuki was a defense facility built in the mid-seventh century. It stretched from current Onojo City to Dazaifu City, Fukuoka Prefecture.
It was designated as a historic site, Mizuki-ato (the Mizuki remains) on March 3, 1921. The designated area of the site is 150,805.80 square meters.
According to the "Nihonshoki" (Chronicles of Japan) cited as follows, there was a grave concern for safety assurance in the background of the construction of the Mizuki.
In 663, Japan, supporting Paekche, was defeated the allied forces of Tang dynasty and Shilla in Korean Peninsula (the Battle of Hakusonko).
At that time, Prince Naka no Oe ruled without official accession to the Chrysanthemum Throne
He had the Mizuki build in 664, the following year, expecting Tang and Shilla invade Dazaifu further from Hakata-wan bay.
In the following year, 665, he ordered to build Kodai Sanjo (ancient Korean-style mountain castles) from Northern Kyushu to the coast of the Inland Sea including Ono-jo Castle (Chikuzen Province), Kii-jo Castle and Nagatonoki Castle.
He transferred the capital to an inland area, Omi Otsu no Miya, in 667.
The beginning of the following year, Prince Naka no Oe finally ascended throne as Emperor Tenchi.
In later years, at the Bunei War (the first Mongolian Invasion) in 1274, the Mizuki was renovated as a defense line against the Mongol army. However, the fortress never became a battlefield.
Structure and intended purpose
The Mizuki is made of a linear moat and dorui (earthen walls for fortification), which used to work as defense line to protect Dazaifu from attacks from Hakata-wan bay. The dorui was more than 10 meters high, 80 meters wide, and 1.2 kilometers long. The moat on Hakata-wan bay side was 60 meters wide and 4 meters in depth, and filled with water. It is confirmed that there was two openings and gates at the dorui as a result of an excavation. Inside the dorui, there was a wooden gutter for letting water run through the moat from the Mikasa-gawa River.
On the place above ridge in southwest, there is a dorui of 80 meters long called Komizuki (small Mizuki) today. This is considered as the fortress to protect Dazaifu, together with the Mizuki in the main portion.
Another opinion of the intended purpose of Mizuki
There is another opinion of the intended purpose of the Mizuki: It was not a mere castle wall, but it was for emergency. The opinion is that the Mizuki was used to keep water back from the Mikasa-gawa River, and washed out enemy who entered the outside dry moat. However, the opinion is seen as lack in persuasiveness because there was gates and a wooden gutter inconvenient for keeping water back and the existence of Komizuki.
Names still used today
There is a station called 'Mizuki Station' on Kagoshima Main Line of Kyushu Railway Company (JR Kyushu).
In Dazaifu City, there is a place called 'Mizuki.'
In Onojo City, there is a place called 'Komizuki.'
There is a temple of the Jinmon-ryu school of Hokkeshu sect called 'Suijo-ji Temple' in Hiratadai, Kasuga City.