As mentioned previously, Japan hastily set up a defense system after the loss of the Battle of Baekgang. First, a telecommunications network was set up in Tsushima and Iki. When the base in Hakata was retracted inland, it served to block the only route of entry to somewhere important-- Mizuki.
Take a moment to check the location of Mizuki on Google Maps. It lies in the narrow land between two mountains. I’m sure you understand by now how important it was to block this place.
Back then they built a 1.2 km long-wall here. They filled the side towards Hakata with water, like a moat. That’s why they named this place “Mizuki”. It’s said that they finished construction of this extensive project in just one year. Considering the technology of that time, our calculations estimate that it would’ve taken 3500 workers to work 11 hours a day for 319 days to achieve this. Such determination could only be explained by the will of the people to protect their country.
Now take another look at the map. You’ll notice that all of the roads and train tracks going south from Hakata follow the road through Mizuki. Because of this, there are a number of highways that pass through Mizuki, but that just goes to show that since then, people have been required to pass through Mizuki to reach Dazaifu. Pretty interesting how nothing has changed, isn’t it?