What is the beacon tower of Dunhuang Great Wall?

Along the Great Wall, there is a beacon tower every 5 kilometers or so. This is the beacon tower of "ten-mile pier and five-mile pier" written in ancient books.

Every beacon tower is guarded by guards. In case of enemy situation, simmer smoke during the day, light the fire at night, sound the alarm and pass the message. You can see fireworks about 5 kilometers away.

There are more than 80 beacon towers in Dunhuang, and Yumenguan and West Lake are the best preserved. Beacon towers in the Han dynasty were mostly square columns with wide bottom and narrow top, which were mainly built inside the Great Wall.