The original telegraph was a series of towers built across France (see map). The aerials on top of the towers could be used to make shapes. Each shape could be looked up in a code book and deciphered into letters, words, or numbers.
Messages could be sent across vast distances in this manner, passed from operators in one tower to the next. Reception was limited to line of site, but this system had obvious advantages in detecting and responding to foreign military operations.
More information is available here and here.
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