This vat is also called "Tianhai" in the royal family. Ancient buildings are all wood structures. If it's a deep courtyard with a wide door, it must be far from the water source. When the weather is dry, it is easy to cause fire. Two vats were put in the house to store water, so as to draw water in time to put out the fire. Of course, the ancients also believed that water tanks could suppress evil fires. Two water tanks were placed to protect themselves from evil fires and to ward off evil spirits.