The Rise and Fall of the Visual Telegraph (2017)

For the discworld alternative, check the clacks [1].

[1] https://wiki.lspace.org/Clacks

There are many places called Telegraph Hill that used to be semaphore towers.

It’s also fascinating this didn’t existed 300 years sooner (with more towers because of poorer telescopes). Communication of information across a kingdom is so important

If i remember correctly the laser optical transmission tech started as a "laser visual telegraph" between 2 PARC buildings rooftops in the Stanford Research Park here.

Ah, so that's the origin of semáforo in Spanish, which the current meaning is "traffic light". And a semaphore on programming, too.