 At first, the wall was built of mainly dirt and rock and logs. Later, the Chinese built kilns for actually making their own fire-hardened bricks. Now, not only did they build the wall, they built towers and huge gates. And to keep these gates from being knocked down, they put up thick additional walls so that marauding enemies could not bust through. Each tower was manned by 60 men to protect and watch for the enemy. But just how did they communicate between the towers?