almost anything that makes a noise has been used for signaling. cyrus, an ancient persian ruler, established lines of signal towers. at each one, people with powerful voices shouted a message to the next tower, and in this way, news and information was passed on through the kingdom. a kind of drum talk is still used in central africa today, although few who are not natives have been able to understand it. the sender uses a drum that can produce a high or low tone. because the local dialect alternates in these tones, the sender is able to simulate speech with the drums.