Roukoku” means water clock. During the Ryukyu Kingdom Era, there was a water clock inside of the watchtower above the gate.

A water clock functions by using a fixed amount of water flowing down from a box which accumulates water at the top to measure the time. Lower class workers in the castle grounds would take care of the clock, and a taiko drum would be sounded for every hour. The temples around Shurijo would then simultaneously ring the bells on the grounds. This is how the time was told back then.

The most influential politician at the time, Sai On, stated that using the water clock was unreliable and he implemented the use of the sundial. He believed this job to be a “not worth” his time,” and delegated it to the higher level officials in the castle.

Sai On’s main goal was not just to tell time more accurately. Ryukyu at the time had a habit of not paying attention to time which was referred to as “Uchina Time.”Being lenient with time is the cause for a lenient nation. Sai On believed it was an important job to lead his citizens to treat time as important to present his nation as a mighty one.

The sundial today is recreated in the open space past the Roukokumon and referred to as the “nichi’eidai.