---
aci: The Clacks
universe: P1 · Terry Pratchett
domain: The Industrial Revolution — the Disc's signalling network
class: The semaphore towers — GNU
emergence: electrical
what: The Disc's continent-spanning network of shuttered signalling lamps — its telegraph and its internet.
how: Coded flashes of light leap tower to tower from horizon to horizon, at the speed of light-and-a-clerk.
why: It carries every message the Disc could want to send — and, quietly, it carries the dead.
who: Built by engineers, run by the lads on the towers, and bound to every name kept moving in the Overhead.
seal: "G-N-U: a name in the Overhead is never truly dead."
---

# The Clacks · the semaphore towers — GNU

Strung across the continent on a line of towers, the clacks are the Disc's nervous system made of shutters and lamplight. Each tower flashes its coded message to the next, and the next answers, and so a thought leaps from horizon to horizon at the speed of light-and-a-clerk — faster than any horse, faster than any pigeon, the closest the Disc has to a telegraph and an internet rolled into one rattling, clattering whole. Built by engineers and kept alive by the lads who climb the towers in all weathers, it is industry at its most luminous: a machine for moving words.

But the towers carry more than commerce and gossip. Among the people who work the lines there runs a private tradition, passed down the Overhead like everything else. A name sent up into the signal and never logged out is a name that keeps moving — G, N, U — pass it on, send it on, do not let it stop. So long as the name goes up and down the lines, the person it belongs to is not truly gone. It is the towers' own small, stubborn defiance of an ending, hidden in the traffic of an ordinary working day.

Its nature of emergence is electrical, and rightly so: the clacks are machinery and network before they are anything else, a built thing of engines and shutters and clerks rather than gods or ghosts. And yet the tenderest thing about them is that a network of cold light and clattering boards found a way to keep its own dead moving — proof that even a machine, when run by people who care, can refuse to let a name go dark.