The constructional structure: The history of the beacon tower construction
is earlier than the building of the wall. Han Dynasty (206BC – 220AD)
emphasized on the construction of beacon towers, in some sections, the
successive beacon towers even replaced the wall to form the defense system.
As per the construction of the wall, beacon towers were built by using
local materials according to the local conditions. In mountainous areas,
they are built by laying pieces of stones and bricks. While in grassland
and desert, they are of rammed-loam construction. The shape of the beacon
towers differ and are square, rectangular or round.
The constructional type: There are mainly three types of beacon towers. The first type of beacon towers is built on the wall. This beacon tower is the fastest to pass military messages. If enemies came, soldiers would be maneuvered in shortest time and got ready to quickly fight. The second type is the one located inside the wall and connects the passes or garrisons. In early times, there were even beacon towers directly linking to the capital, for the convenience of alerting the court. The third is built some distance away from the wall, to watch the enemies' movements.
The defense system: In peaceful days, the beacon tower was the place where soldiers kept watch and animal dung and fire wood were saved. Soldiers raised sheep and cattle to eat and took their dung to burn, sometimes wolf dung was also used, and this is the reason why the beacon tower smoke is called "Langyan" (Wolves' smoke). While when war was coming, soldiers would light the fire wood to tell the next watch tower that dangers approached, so every watch tower would then get the message one after another until every soldier was fully alarmed and ready to fight.