The Kirzierduoha Beacon Fire Tower is in Northwest China's Xinjiang Uygur autonomous region. Being the oldest and most effective original telegram, beacon towers are the most important component of the defensive project on the Great Wall. They are built continually to pass military messages. In ancient times, if intruders approached, soldiers on the wall would create smoke in the daytime and light a fire at night to warn their troops.[Photo/CFP]