One of a range of enigmatic devices which are highly prized by Dwarfs, appearing first in Thud!. Most known examples are now in the possession of dwarfs of high station such as Grags or kings. Such devices are rare and highly prized, and the Dwarfs will even go to the extreme of tunneling under Ankh-Morpork to locate one very special one...
A related device is the axle.
The origins of these technomantic Devices remain shrouded in mystery. Dwarfs (reluctantly) admit they did not make them and have no idea at all as to how they work. They are generally found, once in a blue moon, in deep and inaccessible geological strata. Drawn first by their intrinsic beauty and the fact that something as regularly cubic as this is not likely to be a natural artefact, it took centuries of trial and error before the Dwarfs began to realise what they are for.
Cubes are made of an extremely tough metal which resembles heavily patinaed bronze, they range in size from less than two inches to six inches. They are adorned with green and blue lines, which flicker magically in the dark. They have no obvious controls or buttons.
It must have taken a lot of random prodding and poking, or maybe even a lucky accident, for Dwarfs to realise they function as a sort of tape-recorder. Push this seemingly "just the same as anywhere else" part of this facet of the cube, and it will record. Push another seemingly random spot and it will stop recording. Press here and it will play back. And this is even before we consider the sound-activated ones, which need a key word or sound to make them go. This code can be a sound, a word, an incident or anything else. However once the cube has been activated it is usually programmed to respond to a spoken dwarfish word and its contents deleted to make room for words, some cubes can store at least ten years worth of sound.
The dwarfs use special hearing devices to search for cubes which might be babbling forlornly in the dark for years.
Mining on Roundworld has often thrown up anomalies that archaeology has been at a loss to explain. Several regular metal cubes (as far as anyone can tell, totally inert ones) were located in rock strata thought to be many milions of years old. [] Although rock strata may move faster than we think: a German U-boat that was lost off the Turkish coast in 1917 was rediscovered eighty years later. One mile inland and 800 metres underground. Unless it was moved by trolls, the inescapable conclusion is that the Turkish coast is less "fixed" than we think and some sort of natural shifting of the rock layers took the wreck inland. See Fortean Times.
Fortean thinkers have often speculated as to whether we have been visited by aliens. The metal cubes found in the coal mine are often trotted out as evidence of this... holes in the pockets of those futuristic one-piece silver jumpsuits? Although Erich von Daniken speculated they could be some sort of sophisticated alien machines that the human race is simply too primitive to understand. (Well, he would, wouldn't he?)
A third possibility concerns the plot of Pterry's sci-fi novel Strata, which is also about a Discworld, but one which exists independently of elephants and Turtle. This turns out to be an artificial construct powered by sophisticated machinery, which, when the heroes of the story are stranded there, turns out to be neglected and on the point of breaking down. Surely not?