Asuka Mizuochi remains （Asuka Village, Takaichi District, Nara Prefecture）

　It is one of the ruins of the Asuka period that are dotted around the Asuka region, then Mizuochi means "Water Clock."

　It is assumed to be the remains of the "Rokokudai" remains in historical documents, and experts thought to have been used around 650 to 660.

　Even though it is called a water clock, but it is a large-scale piece of equipment.

　Connect several tanks in a staircase pattern and fill the top tank with water. The collected water is poured into the lower tanks at a constant flow rate. It is a mechanism that allows people at the time to know the passage of time by the flow rate of water collected in the lower tank.

Ruins of Rokokudai

　Although it is a very primitive equipment at first glance, but it was very useful for ancient Japan. Where until the only way to know the approximate passage of time was from "Sundials" and "The Position of the Sun and Stars Visually." It was the most advanced technology at the time, allowing people at the time to tell the time quite accurately.

　It is said that the Rokokudai was also adopted by Prince of Nakanooe through the "Envoys to Sui" and "Envoys to Tang Dynasty."

　Why did the imperial court in the Asuka period need a Rokokudai?

　From a practical perspective, it is "Time management for working a the Imperial Court." In addition to physical information such as arrival and departure from court times and lunch break times, the Rokokudai also lets people at the time know when it's time with the sound of a drum.

　Work assessment based on accurate working hours is an important tool for the Imperial Court, which aims to become a state of the system of centralized administration.

　At its core, the idea of "Control over time" introduced from China also had an influence.

　The idea is that the head of the dynasty as the emperor rules over everything in this world.

　The emperor believed that he was an entity that controlled not only the government officials and residents or forest and rivers something as material aspects, but also "Could Controlled Time."

　So how does time govern?

　Let people as the time know what time it is now and act accordingly. In other words, time management was considered to be equivalent to time control. To improve time management, the emperor needed a water clock that would tell them the exact time.

　The same goes for "Calendar" and "The name of an era."

　When a year begins and ends, also what month and day it is determined by the calendar published by the Imperial Court.

　Similarly, the name of an era also depends on what year as what era.

　Accepting the calendars and era names published by the Imperila Court is equivalent to declaring that some people accept the rule of the Imperial Court, and by extension, some people accept the emperor at the top of the court.

　Therefore, when China rebelled, the areas under its control used different era names. Using a different era name was a rejection of imperial rule.