Based upon scientific measurements, the construction date of mizu-shiro (castles on lakes or marshes for defensive reasons) was ninety years earlier than the construction date in mentioned in the "Nihonshoki" (Chronicles of Japan), which was even earlier than the main body of Dazai-fu.
水城の建設等は、理科学的測定によれば『日本書紀』の記述等より90年以上も古くなり、大宰府本体も古くなる可能性がある。