原来这是当时故宫里的一种防火设施。很早以前，人们就想出了在门前放置铜缸雕塑以及时救火的办法，只要时常将水注满，发生火情时就可以随时就近取水灭火。那时，人们称大缸为“门海”。从字面上不难理解。“门海”即是门前之大海。他们认为，门前有了大海就不会再发生火灾了，因此，大缸又被称做“吉祥缸”、“太平缸”。

It turned out that this was a fire prevention facility in the Imperial Palace at that time. A long time ago, people came up with a way to put a Bronze Cylinder sculpture in front of the door and put out the fire in time. As long as the water is filled up frequently, when there is a fire, water can be taken nearby at any time to put out the fire. At that time, people called the VAT "Menhai". It's not hard to understand literally. The "gate sea" is the sea in front of the gate. They believed that there would be no more fire if there was a sea in front of the door. Therefore, the big tank was also called "auspicious tank" and "Taiping tank".

在清代，宫中的铜缸是由内务府统一管理的。每天一早，内务府官员便命杂役从井内汲水，一担一担地把所有大缸灌满，以备防火之用。每年到了小雪季节，宫内的太监就要在铜缸外套上一层特制的棉套，上面再加上厚厚的缸盖。同时在铜缸下的汉白玉石基座里放置一盆炭火，并保证其昼夜不息地燃烧着。这样，通过双重保暖措施，防止缸内的存水结冰。保暖工作一直要到第二年的惊蛰时节才能结束，那时大地回春，气候已经逐渐转暖，太监们就会解去棉套，撤去炭火。为了保证宫中有足够的水源用于灭火，当时在宫中设置了许多大缸。

In the Qing Dynasty, the copper tanks in the palace were under the unified management of the Ministry of internal affairs. Every morning, the officials of the interior government ordered the workers to take water from the well and fill all the big tanks with one load of water for fire prevention. Every year, in the light snow season, the eunuch in the palace will coat the copper cylinder with a special cotton sleeve and a thick cylinder head. At the same time, a basin of carbon fire is placed in the base of the marble under the copper cylinder to ensure that it burns day and night. In this way, double thermal insulation measures are adopted to prevent the water in the cylinder from freezing. The work of keeping warm can not be finished until the second year of hibernation, when the earth returns to spring and the climate has gradually warmed, the eunuchs will remove the cotton padded jacket and the charcoal fire. In order to ensure that there is enough water in the palace to put out the fire, many large tanks were set up in the palace at that time.