How Did the Watchtowers on the Great Wall of China Function?

The Great Wall of China is a 4,000-mile long barricade built to keep invaders out. Stretching across mountains, deserts and grassy plains, it took more than 1,500 years to build, and is today a cultural icon of the Chinese people.

Time Frame

Construction on the Great Wall of China began during the Qin dynasty in the third century B.C. as a series of earthen and wooden fortifications. Construction continued during the ensuing Han dynasty and was completed during the Ming dynasty between 1368 and 1644.

Features

The watchtowers are two-stories tall, with the first floor serving as barracks and storage space and the upper floor acting as a lookout tower and signal beacon.

Significance

Signal fires were used to send messages from tower to tower. One puff of smoke meant 100 enemy soldiers approaching; two puffs meant 500, and each additional puff another 500. It took several hours to send a message the entire length of the Great Wall.

Military Purpose

Cannons were placed on top of the towers to fire at enemy soldiers. If an opposing army scaled the wall, the defenders retreated inside the narrow towers, forcing their enemies to enter single file where they could pick them off one by one.

Different Towers

The watchtowers were not evenly spaced, ranging from less than half a mile to several miles apart. Most towers were square, but some were rectangular and others round, and they were built with various materials, depending on what local supplies were available.

Fun Fact

The signal fires were called langyan, meaning "wolves' smoke" because the fires were sometimes kept burning with wolf dung.