For those unfamiliar with Terry Pratchett's
Discworld series, 'Clacks' are the nickname for the semaphore network on the Discworld, serving as an analogue for telegraphy and the Internet.
The nature of the technology is fairly simple. Large towers, separated by a medium distance of about twenty miles, each house grids of lights with shutters. The grid is used to represent letters and numbers, rather like Braille, and operators in the tower observe messages sent to them and work the shutters to send the message onwards down the line. The 'Clacks' on the Discworld use codes to shorten the characters needed to send a message, and apparently are sophisticated enough to send colour images.
The inspiration for the clacks come from real-life semaphore networks operated in Britain and France around during the Napoleonic Period. These networks were much simpler, had speeds of about two words a minute and were quickly overtaken by telegraphy.
My question is, when was the earliest time that semaphores at a level of sophistication seen in
Discworld were feasible in both a technical and commercial sense? What were the prerequisite technologies, and what did society have to look like to make sustainable use of what is bound to be a very resource-intensive piece of infrastructure?